MSBI (SSIS/SSRS/SSAS) Online Training

Monday, November 24, 2008

SSIS QUESTIONS AND ANSWERS

1.what is a package?
a).a discrete executable unIt of work composed of a collection of control flow and other objects, including data sources, transformations ,process sequence, and rules, errors and event handling, and data destinations.

2.what is a workflow in ssis ?
a).`a workflow is a set of instructions on how to execute tasks.
(It is a set of instructions on how to execute tasks such as sessions, emails and shell commands. a workflow is created form work flow mgr.)

3.what is the diff between control flow Items and data flow Items?
a).the control flow is the highest level control process.It allows you to manage the run-time process the run time process activIties of data flow and other processes wIthin a package.
when we want to extract, transform and load data wIthin a package. you add an ssis dataflow task to the package control flow.

4.what are the main component of ssis(project-archItecture)?
A).ssis archItecture has 4 main components
1.ssis service
2.ssis runtime engine & runtime executables
3.ssis dataflow engine & dataflow components
4.ssis clients

5.different components in ssis package?
a).1.control flow
2.data flow
3.event handler
4.package explorer

containers:::provide structure and scope to your package
types of containers:
i.task host container:the taskhost container services a single task.
ii.sequence container:It can handle the flow of subset of a package and can help you drive a package into smaller more managable process.
uses:-1.grouping tasks so thatyou can disable a part of the package thats no longer needed.
2.narrowing the scope of the variable to a container.
3.managing the property of multiple tasks in one step by setting the properties of the container.
iii.for loop container:evaluates an expression and repeats Its workflow until the expression evaluates to false.
iv.for each loop container:defines a control flow repeatedly by using an enumerator.
the for each loop container repearts the control flow for each member of a specified enemurator.

tasks:::It provide the functionalIty to ur package.
It is a individual unIt of work.

event handler::respond to raised events in your package.

precedence constraints::provide ordinal relationship b/w various Items in ur package.
6.how to deploy the package?
a).to deploy the package first we need to configure some properties.
goto project tab->package properties->we get a window,configure deployment utilIty as "true"
mention the path as "bin/deployment"

7. Connection manager:
a).It is a bridge b/w package object and physical data. It provides logical representation of a connection at design time the properties of the connection mgr describes the physical connection that integration services creates when the package is run.

8. Tell the utilIty to execute (run) the package?
a) In BIDS a package that can be executed in debug mode by using the debug menu or toolbar or from solution explorer.
In production, the package can be executed from the command line or from a Microsoft windows utilIty, or It can be scheduled for automated execution by using the sql server agent.
i).goto->debug menu and select the start debugging button
ii).press F5 key
iii).right click the package and choose execute package.
iv).command prompts utilIties
a).DTExecUI
1. To open command prompt->run->type dtexecui->press enter
2. The execute package utilIty dialog box opens.
3. in that click execute to run the package.
WaIt until the package has executed successfully.
b).DTExec utilIty
1.open the command prompt window.
2.command prompt window->type dtexec/followed by the DTS,SQL,or file option and the package path ,including package name.
3.if the package encryption level is encrypt sensItive wIth password or encrypt all wIth password, use the decrypt option to provide the password.
If no password is included, dtexec will prompt you for the password.
4. Optionally, provide addItional command-line options
5. Press enter.
6. Optionally, view logging and reporting information before closing the command prompt window.
The execute package utilIty dialog box opens.
7. In the execute package utilIty dialog box, click execute package.
WaIt until the package has executed successfully.
v).using sql server mgmt studio to execute package
1. In SSMS right click a package, and then click run package.
Execute package utilIty opens.
2. Execute the package as described previously.

9. How can u design SCD in SSIS?
a) Def:-SCD explains how to capture the changes over the period of time.
This is also known as change data capture.
type1: It keeps the most recent values in the target. It does not maintain the history.
type2: It keeps the full history in the target database. For every update in the source anew record is inserted in the target.
type3: It keeps current & previous information in the target.
in-SSIS:
-------
type1: It can do require re-creating any aggregation that would be affected by the change.
type2: changes can cause a serious inflation in the number of members of a dimension.
type3: as wIth a type 1 change, type 3 change requires a dimension update, so u need to re-process
All aggregations affected after change.

10. How can u handle the errors through the help of logging in SSIS?
a) To create an on error event handler to which you add the log error execute sql task.

11. What is a logfile and how to send log file to mgr?
a) It is especially useful when the package has been deployed to the production environment, and you can not use BIDS and VSA to debug the package.
SSIS enables you to implement logging code through the Dts. Log method.
When the Dts. Log method is called in the script, the SSIS engine will route the message to the log providers that are configured in the containing package.

12. What is environment variable in SSIS?
a) An environment variable configuration sets a package property equal to the value in an environment variable.
Environmental configurations are useful for configuring properties that are dependent on the computer that is executing the package.

13. about multiple configurations?
a) It means including the xml configuration, environment variable, registry entry, parent package variable, SQL Server table, and direct and indirect configuration types.

14. How to provide securIty to packages?
a) In two ways
1. Package encryption
2. Password protection.

15. as per error handling in T/R, which one handle the better performance? Like fail component, redirect row or ignore failure?
a) Redirect row provides better performance for error handling.

16. Staging area??
a) It is a temporary data storage location. Where various data T/R activIties take place. A staging area is a kItchen of data warehouse.

17. Task??
a) An individual unIt of work.
Types:-
.....
1. Active x script task
2. Analysis services execute DDL task
3. Analysis services processing task
4. Bulk insert task *
5. Data flow task *
6. Data mining query task
7. Execute Dts 2000 package task
8. Execute package task *
9. Execute process task
10. Execute sql task *
11. File system task
12. Ftp task
13. Message queue task
14. Script task *
15. Send mail task *
16. Web service task
17. Wmi data reader task
18. Wmi event task
19. Xml task

18. Event handling & logging?
a) You can select the t/r fails and exIts up on an error, or the bad rows can be redirected to a failed
Data flow branch. Ignore failure, redirect row.
Logging also improved there are more than a 12 events that can be logged for each task or package. You can enable partial logging for one task and enable much more detailed logging for billing tasks.
Ex:-on error
On post validate
On progress
On warning
--->log file can be wrItten to usually any connection
Sql profiler
Text files
Sql server
Window event log
Xml file

19. Import & export wizard?
a) Easiest method to move data from sources like oracle, db2, sql server.
Right click on database name->goto task->import and export wizard
Select the source
Select the destination
Query copy of tables
Execute
Finish

20.solution explorer?
after creating project
project name
-data source
-data source views
-packages
-miscellaneous

21. Precedence constraints?
a) Constraints that link executable, container, and tasks wIthin the package control flow and specify condItion that determine the sequence
And condItions for determine whether executable run.

22. Data pipeline?
a) The memory based, multIthreaded, buffered t/r process flow data through an SSIS data flow task during package execution.

23. TRANSFORMATIONS??
It is an object that generates, modifies, or passes data.
1.AGGEGATE T/R:-It applies an aggregate function to grouped records and produces new output records from aggregated results.
2.AUDIT T/R:-the t/r adds the value of a system variable, such as machine name or execution instance GUID to a new output column.
3.CHARACTER MAP T/R:-this t/r makes string data changes such as changing data from lower case to upper case.
4.CONDITIONAL SPLIT:-It separate input rows into separate output data pipelines based on the boolian expressions configured for each output.
5.COPY COLUMN:-add a copy of column to the t/r output we can later transform the copy keeping the original for audIting personal
6.DATA CONVERSION:-converts a columns data type to another data type.
7.DATA MINING QUERY:-perform a data mining query against analysis services.
8.DERIVED COLUMN:-create a new derive column calculated from expression.
9.EXPORT COLUMN:-It allows you to export a column from the data flow to a file.
10.FUZZY GROUPING:-perform data cleansing by finding rows that are likely duplicates.
11.FUZZY LOOKUP:-matches and standardizes data based on fuzzy logic.
eg:-transform the name jon to john
12.IMPORT COLUMN:-reads the dat from a file & adds It into a dataflow.
13.LOOKUP:-perform the lookup of data tobe used later in a transform.
ex:-t/f to lookup a cIty based on zipcode.
1.getting a related value from a table using a key column value
2.update slowly changing dimension table
3.to check whether records already exist in the table.
14.MERGE:-merges two sorted data sets into a single data set into a single data flow.
15.MERGE JOIN:-merges two data sets into a single dataset using a join junction.
16.MULTI CAST:-sends a copy of two datato an addItional path in the workflow.
17.ROW COUNT:-stores the rows count from the data flow into a variable.
18.ROW SAMPLING:-captures the sample of data from the dataflow by using a row count of the total rows in dataflow.
19.ROW SAMPLING:-captures the sample of the data from the data flow by using a row count of the total rows in data flow.
20.UNION ALL:-merge multiple data sets into a single dataset.
21.PIVOT:-converts rows into columns
22.UNPIVOT:-converts columns into rows

24. Batch?
a) A batch is defined as group of sessions. Those are 2 types.
1. Parallel batch processing
2. Sequential batch processing

-----For executing the package we can use "execute package utilIty"----

----for deploying the package we can use "package deployment utilIty"—


SSRS:--

1. What are the main components of reporting services?
a) Report designer, report server, report manager, report user.

2. Where can u publish the report?
a) By using report designer or publish reports on report server.

3. What are the necessIty things for creating matrix report?
a) Page, column, row, details

4. for generating reports which is used like RDBMS OR CUBE?
a) Depends on data

5. What is assembly code in SSRS?
a)

6. What is Rdl file?
a) Rdl is a Report DefinItion Language. Every report is saving wIth Rdl Extension.

7. How can u create a job?
a) Job is a group of reports.
The reports can be processed eIther sequentially or parallel.

SSAS:-

1. What are the fixed measure and calculated measure?
a) Normally we used fixed measures in SSIS mainly for calculating measures.
Where as calculated measures uses in SSAS, while creating cube we can mention this calculated measure in the OLAP.

2. What are measures?
a) Measures are numeric data based on columns in a fact table.

3. What are cubes?
a) Cubes are data processing unIts composed of fact tables and dimensions from the data warehouse. They provided multidimensional analysis.

4. What are virtual cubes?
These are combination of one or more real cubes and require no disk space to store them. They store only definItion and not the data.






DATAWARE HOUSE CONCEPTS:-

1. Diff b/w OLTP AND OLAP?
A)
OLTP OLAP
_________________________________________
1.transactional processing 1.query processing
2.time sensItive 2.history oriented
3. Operator & clerks view 3.Managers, CEOs, PM’s views
4. organized by transaction 4.organized by subjects
(Order, input, inventory) (product, customer)
5.relatively smaller DB 5.large DB size
6.volatile data 6.non-volatile
7.stores all data 7.stores relevant data
8. Not flexible 8.flexible

2. Diff b/w star schema and snowflake?
a) STAR SCHEMA SNOWFLAKE
_____________________________________
1.centrally located fact table 1.centraly located fact table
surrounded by de normalise surronded by the normalized
Dimensions. dimension table.
2.all dimensions will be link 2.all dim link wIth each other (or)
directly wIth fact table. 1-N relationship wIth other table.
3.It is easy to understand by 3.It is diff to understand.
end user or tech people 4.It is diff to retrieve the data while
4.We can easily retrieve data parsing the query against the facts n dim.
By passing the simple queries.
5.increase the query perform- 5.more joins.
ance because It involve less
Joins.

What are fact tables?
a) A fact table is a table that contains summarized numerical (facts) and historical data.
This fact table has a foreign key-primary key relation wIth a dimension table. the fact table maintains the information in 3rd normal form.

3. Types of facts?
a)
1. AddItive:-able to add the facts along wIth all the dimensions
-discrete numerical measures.
-Ex:-retail sales in $
2. semi addItive:-snapshot taken at a point in time
- Measure of intensIty
-not addItive along time dimensions
ex:-account balance, inventory balance
3.non-addItive:-numerical measures that can't be added across any dimensions.
-intensIty measure arranged across all dimension
ex:-room temperatures, averages


4. Data warehouse?
a) A data ware house is a collection of data marts representing historical data from diff operational data sources (OLTP).
The data from these OLTP are structured and optimized for querying and data analysis in a data warehouse.

5. Data mart?
a) A data mart is a subset of a data warehouse that can provide data for reporting and analysis on a section, unIt or a department like sales dept, hr dept.

6. What is OLAP?
a) OLAP stands for online analytical processing. It uses databases tables (fact and dimension table) to enable multi dimensional viewing, analysis and querying of large amount of data.

7. What is OLTP?
a) OLTP stands for online transactional processing. Except data warehouse databases the other databases are OLTP.
These OLTP uses normalized schema structure.
These OLTP databases are designed for recording the daily operations and transactions of a business.

8. What are dimensions?
Dimensions are categories by which summarized data can be viewed. For example a profIt summary fact table can be viewed by a time dimension.

9. What are conformed dimension?
a) The dimensions which are reusable and fixed in nature. Example customer, time, geography dimensions.

10. Staging area?
a) It is a temporary data storage location, where various data t/r activIties take place.

11. Fact grain(granularIty)?
a) The grain of fact is defined as the level at which the fact information is stored in a fact table.

12. What is a fact less fact table?
a) The fact table which does not contain facts is called as fact table.
Generally when we need to combine two data marts, then one data mart will have a fact less fact table and other one wIth common fact table.

13. What are measures?
a) Measures are numeric data based on columns in a fact table.

14. What are cubes?
a) Cubes are data processing unIts composed of fact tables and dimensions from the data warehouse. They provided multidimensional analysis.

15. What are virtual cubes?
These are combination of one or more real cubes and require no disk space to store them. they store only definItion and not hte data.
16.SCD's?
a)
type-I(current data)
type-II(full historical information& Current data)
type-III(Current data & Recent data)

SQL-SERVER-2005:-

1. Surrogate key?
a)It is an artificial or synthetic key that is used as a substItute for a natural keys.
It is just a unique identifier or number for each row that can be used for the primary key to the table.
(It is a sequence generate key which is assigned to be a primary key in the system(table)).

2.primary key?
a)can be used to uniquely identify every row of the table.
------unique + not null-------

3.foreign key?
a)It is a column r combination of columns that contain values that are found in primary key of some table.
It may be null, not unique.

4.composIte key?
a)It is a primary key consisting of more than one column.

4. indexes?
a) It is an access strategy that is a way to sort and search records in the table.
Indexes are essential to improve the speed wIth which records can be located and retrieved from a table.
Types: - cluster index (can create only one index on table)
Non-cluster index (can create 249 indexes on table)
Unique index
Composite index
(Simple index, reverse key index, bitmap index, function index)

5. View?
a) It is used for data security reason
To reduce the redundant data.

6. Cluster?
a) 1-many access path.
Clusters are used to store data from diff tables in the same physical data blocks.

7. Sequences?
a) It is used to quickest way to retrieve the data.

8. Cursors?
a) Implicit cursor
Explicit cursor
Parameter cursor

9. Triggers?
a) Row trigger
Statement trigger
10. Transactions?
Save point
Commit & rollback.
11. Security?
a) Encryption
Locking
Level of lockings row level, page level, table level
12.constraints?
a)primary->
foreign(reference)->
check->
unique->
13. Diff b/w having and where?
a) after performing 'group by' operation 'having wil again filter the records based on having condItion
'where' is used to filter the data based on a condItion and It applies to retrive on a particular column.
14. Joins?
a) Join can combine the information from two tables into a single unit.
inner join:-
they matched the records together based on one or more common fields(matched-records only).
outer join:-

full join:-It combines the all rows on both sides of the join.
cross join:-
15. Union & union-all?
a) Union:-columns, data types should be same
Select distinct values
Remove duplicates
Union-all:-displays all the rows exact & duplicates.
16. Diff b/w drop, delete & truncate?
delete:-delete all rows at a time
delete a single row data based on condItion.
memory allocation will be there
structure will be there
truncate:-delete all rows at a time
can't delete single row at a time
memory allocation deleted
table structure wil be there
drop :- delete all rows at a time
can't delete single row at a time
memory allocation can be deleted
table structure also do deleted
----------------queries---------------
1.Nth highest salary?
select rownum,sal from (select rownum,sal from emp order by sal desc)
group by rownum,sal having rownum=&N; (OR)
select top 1 sal from (select top 10 sal from emp order by sal desc) A

Sql Server Interview Questions And Answers

SQL-Server Interview Questions
What is RDBMS?Relational Data Base Management Systems (RDBMS) are database management systems that maintain data records and indices in tables. Relationships may be created and maintained across and among the data and tables. In a relational database, relationships between data items are expressed by means of tables. Interdependencies among these tables are expressed by data values rather than by pointers. This allows a high degree of data independence. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage.
What is normalization?Database normalization is a data design and organization processes applied to data structures based on rules that help build relational databases. In relational database design, the process of organizing data to minimize redundancy. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables. The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships.What are different normalization forms?
1NF: Eliminate Repeating GroupsMake a separate table for each set of related attributes, and give each table a primary key. Each field contains at most one value from its attribute domain.2NF: Eliminate Redundant DataIf an attribute depends on only part of a multi-valued key, remove it to a separate table.3NF: Eliminate Columns Not Dependent On Key If attributes do not contribute to a description of the key, remove them to a separate table. All attributes must be directly dependent on the primary keyBCNF: Boyce-Codd Normal FormIf there are non-trivial dependencies between candidate key attributes, separate them out into distinct tables.4NF: Isolate Independent Multiple RelationshipsNo table may contain two or more 1:n or n:m relationships that are not directly related.5NF: Isolate Semantically Related Multiple Relationships There may be practical constrains on information that justify separating logically related many-to-many relationships.ONF: Optimal Normal FormA model limited to only simple (elemental) facts, as expressed in Object Role Model notation.DKNF: Domain-Key Normal FormA model free from all modification anomalies.
Remember, these normalization guidelines are cumulative. For a database to be in 3NF, it must first fulfill all the criteria of a 2NF and 1NF database.
What is Stored Procedure?A stored procedure is a named group of SQL statements that have been previously created and stored in the server database. Stored procedures accept input parameters so that a single procedure can be used over the network by several clients using different input data. And when the procedure is modified, all clients automatically get the new version. Stored procedures reduce network traffic and improve performance. Stored procedures can be used to help ensure the integrity of the database.e.g. sp_helpdb, sp_renamedb, sp_depends etc.
What is Trigger?A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE) occurs. Triggers are stored in and managed by the DBMS.Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed; the DBMS automatically fires the trigger as a result of a data modification to the associated table. Triggers can be viewed as similar to stored procedures in that both consist of procedural logic that is stored at the database level. Stored procedures, however, are not event-drive and are not attached to a specific table as triggers are. Stored procedures are explicitly executed by invoking a CALL to the procedure while triggers are implicitly executed. In addition, triggers can also execute stored procedures.Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the trigger is fired because of data modification it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger.
What is View?A simple view can be thought of as a subset of a table. It can be used for retrieving data, as well as updating or deleting rows. Rows updated or deleted in the view are updated or deleted in the table the view was created with. It should also be noted that as data in the original table changes, so does data in the view, as views are the way to look at part of the original table. The results of using a view are not permanently stored in the database. The data accessed through a view is actually constructed using standard T-SQL select command and can come from one to many different base tables or even other views.
What is Index?An index is a physical structure containing pointers to the data. Indices are created in an existing table to locate rows more quickly and efficiently. It is possible to create an index on one or more columns of a table, and each index is given a name. The users cannot see the indexes, they are just used to speed up queries. Effective indexes are one of the best ways to improve performance in a database application. A table scan happens when there is no index available to help a query. In a table scan SQL Server examines every row in the table to satisfy the query results. Table scans are sometimes unavoidable, but on large tables, scans have a terrific impact on performance.
Clustered indexes define the physical sorting of a database table’s rows in the storage media. For this reason, each database table may have only one clustered index.Non-clustered indexes are created outside of the database table and contain a sorted list of references to the table itself.
What is the difference between clustered and a non-clustered index?A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.
A nonclustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a nonclustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.
What are the different index configurations a table can have?A table can have one of the following index configurations:
No indexesA clustered indexA clustered index and many nonclustered indexesA nonclustered indexMany nonclustered indexes
What is cursors?Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time.
In order to work with a cursor we need to perform some steps in the following order:
Declare cursorOpen cursorFetch row from the cursorProcess fetched rowClose cursorDeallocate cursor
What is the use of DBCC commands?DBCC stands for database consistency checker. We use these commands to check the consistency of the databases, i.e., maintenance, validation task and status checks.E.g. DBCC CHECKDB - Ensures that tables in the db and the indexes are correctly linked.DBCC CHECKALLOC - To check that all pages in a db are correctly allocated.DBCC CHECKFILEGROUP - Checks all tables file group for any damage.
What is a Linked Server?Linked Servers is a concept in SQL Server by which we can add other SQL Server to a Group and query both the SQL Server dbs using T-SQL Statements. With a linked server, you can create very clean, easy to follow, SQL statements that allow remote data to be retrieved, joined and combined with local data.Storped Procedure sp_addlinkedserver, sp_addlinkedsrvlogin will be used add new Linked Server.
What is Collation?Collation refers to a set of rules that determine how data is sorted and compared. Character data is sorted using rules that define the correct character sequence, with options for specifying case-sensitivity, accent marks, kana character types and character width.
What are different type of Collation Sensitivity?Case sensitivityA and a, B and b, etc.
Accent sensitivitya and á, o and ó, etc.
Kana SensitivityWhen Japanese kana characters Hiragana and Katakana are treated differently, it is called Kana sensitive.
Width sensitivityWhen a single-byte character (half-width) and the same character when represented as a double-byte character (full-width) are treated differently then it is width sensitive.
What’s the difference between a primary key and a unique key?Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only.
How to implement one-to-one, one-to-many and many-to-many relationships while designing tables?One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships.One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships.Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.
What is a NOLOCK?Using the NOLOCK query optimiser hint is generally considered good practice in order to improve concurrency on a busy system. When the NOLOCK hint is included in a SELECT statement, no locks are taken when data is read. The result is a Dirty Read, which means that another process could be updating the data at the exact time you are reading it. There are no guarantees that your query will retrieve the most recent data. The advantage to performance is that your reading of data will not block updates from taking place, and updates will not block your reading of data. SELECT statements take Shared (Read) locks. This means that multiple SELECT statements are allowed simultaneous access, but other processes are blocked from modifying the data. The updates will queue until all the reads have completed, and reads requested after the update will wait for the updates to complete. The result to your system is delay(blocking).
What is difference between DELETE & TRUNCATE commands?Delete command removes the rows from a table based on the condition that we provide with a WHERE clause. Truncate will actually remove all the rows from a table and there will be no data in the table after we run the truncate command.
TRUNCATETRUNCATE is faster and uses fewer system and transaction log resources than DELETE.TRUNCATE removes the data by deallocating the data pages used to store the table’s data, and only the page deallocations are recorded in the transaction log.TRUNCATE removes all rows from a table, but the table structure and its columns, constraints, indexes and so on remain. The counter used by an identity for new rows is reset to the seed for the column.You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint.Because TRUNCATE TABLE is not logged, it cannot activate a trigger.TRUNCATE can not be Rolled back using logs.TRUNCATE is DDL Command.TRUNCATE Resets identity of the table.
DELETEDELETE removes rows one at a time and records an entry in the transaction log for each deleted row.If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement.DELETE Can be used with or without a WHERE clauseDELETE Activates Triggers.DELETE Can be Rolled back using logs.DELETE is DML Command.DELETE does not reset identity of the table.
Difference between Function and Stored Procedure?UDF can be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section where as Stored procedures cannot be.UDFs that return tables can be treated as another rowset. This can be used in JOINs with other tables.Inline UDF’s can be though of as views that take parameters and can be used in JOINs and other Rowset operations.
When is the use of UPDATE_STATISTICS command?This command is basically used when a large processing of data has occurred. If a large amount of deletions any modification or Bulk Copy into the tables has occurred, it has to update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.
What types of Joins are possible with Sql Server?Joins are used in queries to explain how different tables are related. Joins also let you select data from a table depending upon data from another table.Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.
What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?Specifies a search condition for a group or an aggregate. HAVING can be used only with the SELECT statement. HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE clause. Having Clause is basically used only with the GROUP BY function in a query. WHERE Clause is applied to each row before they are part of the GROUP BY function in a query. HAVING criteria is applied after the the grouping of rows has occurred.
What is sub-query? Explain properties of sub-query.Sub-queries are often referred to as sub-selects, as they allow a SELECT statement to be executed arbitrarily within the body of another SQL statement. A sub-query is executed by enclosing it in a set of parentheses. Sub-queries are generally used to return a single row as an atomic value, though they may be used to compare values against multiple rows with the IN keyword.
A subquery is a SELECT statement that is nested within another T-SQL statement. A subquery SELECT statement if executed independently of the T-SQL statement, in which it is nested, will return a result set. Meaning a subquery SELECT statement can standalone and is not depended on the statement in which it is nested. A subquery SELECT statement can return any number of values, and can be found in, the column list of a SELECT statement, a FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL statement. A Subquery can also be used as a parameter to a function call. Basically a subquery can be used anywhere an expression can be used.
Properties of Sub-QueryA subquery must be enclosed in the parenthesis.A subquery must be put in the right hand of the comparison operator, andA subquery cannot contain a ORDER-BY clause.A query can contain more than one sub-queries.
What are types of sub-queries?Single-row subquery, where the subquery returns only one row.Multiple-row subquery, where the subquery returns multiple rows,.andMultiple column subquery, where the subquery returns multiple columns.
What is SQL Profiler?SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft SQL Server. You can capture and save data about each event to a file or SQL Server table to analyze later. For example, you can monitor a production environment to see which stored procedures are hampering performances by executing too slowly.
Use SQL Profiler to monitor only the events in which you are interested. If traces are becoming too large, you can filter them based on the information you want, so that only a subset of the event data is collected. Monitoring too many events adds overhead to the server and the monitoring process and can cause the trace file or trace table to grow very large, especially when the monitoring process takes place over a long period of time.
What is User Defined Functions?User-Defined Functions allow to define its own T-SQL functions that can accept 0 or more parameters and return a single scalar data value or a table data type.
What kind of User-Defined Functions can be created?There are three types of User-Defined functions in SQL Server 2000 and they are Scalar, Inline Table-Valued and Multi-statement Table-valued.
Scalar User-Defined FunctionA Scalar user-defined function returns one of the scalar data types. Text, ntext, image and timestamp data types are not supported. These are the type of user-defined functions that most developers are used to in other programming languages. You pass in 0 to many parameters and you get a return value.
Inline Table-Value User-Defined FunctionAn Inline Table-Value user-defined function returns a table data type and is an exceptional alternative to a view as the user-defined function can pass parameters into a T-SQL select command and in essence provide us with a parameterized, non-updateable view of the underlying tables.
Multi-statement Table-Value User-Defined FunctionA Multi-Statement Table-Value user-defined function returns a table and is also an exceptional alternative to a view as the function can support multiple T-SQL statements to build the final result where the view is limited to a single SELECT statement. Also, the ability to pass parameters into a T-SQL select command or a group of them gives us the capability to in essence create a parameterized, non-updateable view of the data in the underlying tables. Within the create function command you must define the table structure that is being returned. After creating this type of user-defined function, It can be used in the FROM clause of a T-SQL command unlike the behavior found when using a stored procedure which can also return record sets.
Which TCP/IP port does SQL Server run on? How can it be changed?SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties –> Port number.both on client and the server.
What are the authentication modes in SQL Server? How can it be changed?Windows mode and mixed mode (SQL & Windows).
To change authentication mode in SQL Server click Start, Programs, and Microsoft SQL Server and click SQL Enterprise Manager to run SQL Enterprise Manager from the Microsoft SQL Server program group. Select the server then from the Tools menu select SQL Server Configuration Properties, and choose the Security page.
Where SQL server user’s names and passwords are are stored in sql server?They get stored in master db in the sysxlogins table.
Which command using Query Analyzer will give you the version of SQL server and operating system? SELECT SERVERPROPERTY ('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY ('edition')
What is SQL server agent?SQL Server agent plays an important role in the day-to-day tasks of a database administrator (DBA). It is often overlooked as one of the main tools for SQL Server management. Its purpose is to ease the implementation of tasks for the DBA, with its full-function scheduling engine, which allows you to schedule your own jobs and scripts.
Can a stored procedure call itself or recursive stored procedure? How many levels SP nesting possible?Yes. Because Transact-SQL supports recursion, you can write stored procedures that call themselves. Recursion can be defined as a method of problem solving wherein the solution is arrived at by repetitively applying it to subsets of the problem. A common application of recursive logic is to perform numeric computations that lend themselves to repetitive evaluation by the same processing steps. Stored procedures are nested when one stored procedure calls another or executes managed code by referencing a CLR routine, type, or aggregate. You can nest stored procedures and managed code references up to 32 levels.
What is @@ERROR?The @@ERROR automatic variable returns the error code of the last Transact-SQL statement. If there was no error, @@ERROR returns zero. Because @@ERROR is reset after each Transact-SQL statement, it must be saved to a variable if it is needed to process it further after checking it.
What is Raiseerror? Stored procedures report errors to client applications via the RAISERROR command. RAISERROR doesn’t change the flow of a procedure; it merely displays an error message, sets the @@ERROR automatic variable, and optionally writes the message to the SQL Server error log and the NT application event log.
What is log shipping?Log shipping is the process of automating the backup of database and transaction log files on a production SQL server, and then restoring them onto a standby server. Enterprise Editions only supports log shipping. In log shipping the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db can be used this as the Disaster Recovery plan. The key feature of log shipping is those is will automatically backup transaction logs throughout the day and automatically restore them on the standby server at defined interval.
What is the difference between a local and a global variable?A local temporary table exists only for the duration of a connection or, if defined inside a compound statement, for the duration of the compound statement.
A global temporary table remains in the database permanently, but the rows exist only within a given connection. When connections are closed, the data in the global temporary table disappears. However, the table definition remains with the database for access when database is opened next time.
What command do we use to rename a db? sp_renamedb ‘oldname’, ‘newname’If someone is using db it will not accept sp_renmaedb. In that case first bring db to single user using sp_dboptions. Use sp_renamedb to rename database. Use sp_dboptions to bring database to multi user mode.
What are sp_configure commands and set commands?Use sp_configure to display or change server-level settings. To change database-level settings, use ALTER DATABASE. To change settings that affect only the current user session, use the SET statement.
What are the different types of replication? Explain.The SQL Server 2000-supported replication types are as follows:
Transactional
Snapshot
Merge
Snapshot replication distributes data exactly as it appears at a specific moment in time and does not monitor for updates to the data. Snapshot replication is best used as a method for replicating data that changes infrequently or where the most up-to-date values (low latency) are not a requirement. When synchronization occurs, the entire snapshot is generated and sent to Subscribers.
Transactional replication, an initial snapshot of data is applied at Subscribers, and then when data modifications are made at the Publisher, the individual transactions are captured and propagated to Subscribers.
Merge replication is the process of distributing data from Publisher to Subscribers, allowing the Publisher and Subscribers to make updates while connected or disconnected, and then merging the updates between sites when they are connected.
What are the OS services that the SQL Server installation adds?MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac co-ordinator)
What are three SQL keywords used to change or set someone’s permissions?GRANT, DENY, and REVOKE.
What does it mean to have quoted_identifier on? What are the implications of having it off?When SET QUOTED_IDENTIFIER is ON, identifiers can be delimited by double quotation marks, and literals must be delimited by single quotation marks. When SET QUOTED_IDENTIFIER is OFF, identifiers cannot be quoted and must follow all Transact-SQL rules for identifiers.What is the STUFF function and how does it differ from the REPLACE function? STUFF function to overwrite existing characters. Using this syntax, STUFF (string_expression, start, length, replacement_characters), string_expression is the string that will have characters substituted, start is the starting position, length is the number of characters in the string that are substituted, and replacement_characters are the new characters interjected into the string.REPLACE function to replace existing characters of all occurance. Using this syntax REPLACE (string_expression, search_string, replacement_string), where every incidence of search_string found in the string_expression will be replaced with replacement_string.
Using query analyzer, name 3 ways to get an accurate count of the number of records in a table?SELECT * FROM table1SELECT COUNT (*) FROM table1SELECT rows FROM sysindexes WHERE id = OBJECT_ID (table1) AND indid < 2
How to rebuild Master Database?Shutdown Microsoft SQL Server 2000 and then run Rebuildm.exe. This is located in the Program Files\Microsoft SQL Server\80\Tools\Binn directory.In the Rebuild Master dialog box, click Browse.In the Browse for Folder dialog box, select the \Data folder on the SQL Server 2000 compact disc or in the shared network directory from which SQL Server 2000 was installed, and then click OK.Click Settings. In the Collation Settings dialog box, verify or change settings used for the master database and all other databases.Initially, the default collation settings are shown, but these may not match the collation selected during setup. You can select the same settings used during setup or select new collation settings. When done, click OK.In the Rebuild Master dialog box, click Rebuild to start the process.The Rebuild Master utility reinstalls the master database.To continue, you may need to stop a server that is running.Source: http://msdn2.microsoft.com/en-us/library/aa197950(SQL.80).aspx
What are the basic functions for master, msdb, model, tempdb databases?The Master database holds information for all databases located on the SQL Server instance and is the glue that holds the engine together. Because SQL Server cannot start without a functioning master database, you must administer this database with care.The msdb database stores information regarding database backups, SQL Agent information, DTS packages, SQL Server jobs, and some replication information such as for log shipping.The tempdb holds temporary objects such as global and local temporary tables and stored procedures.The model is essentially a template database used in the creation of any new user database created in the instance.
What are primary keys and foreign keys? Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental of all keys and constraints. A table can have only one Primary key.Foreign keys are both a method of ensuring data integrity and a manifestation of the relationship between tables.
What is data integrity? Explain constraints?Data integrity is an important feature in SQL Server. When used properly, it ensures that data is accurate, correct, and valid. It also acts as a trap for otherwise undetectable bugs within applications.A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should have a primary key constraint to uniquely identify each row and only one primary key constraint can be created for each table. The primary key constraints are used to enforce entity integrity.
A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.
A FOREIGN KEY constraint prevents any actions that would destroy links between tables with the corresponding data values. A foreign key in one table points to a primary key in another table. Foreign keys prevent actions that would leave rows with foreign key values when there are no primary keys with that value. The foreign key constraints are used to enforce referential integrity.
A CHECK constraint is used to limit the values that can be placed in a column. The check constraints are used to enforce domain integrity.
A NOT NULL constraint enforces that the column will not accept null values. The not null constraints are used to enforce domain integrity, as the check constraints.
What are the properties of the Relational tables?Relational tables have six properties:
Values are atomic.
Column values are of the same kind.
Each row is unique.
The sequence of columns is insignificant.
The sequence of rows is insignificant.
Each column must have a unique name.
What is De-normalization?De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. It is sometimes necessary because current DBMSs implement the relational model poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.
How to get @@error and @@rowcount at the same time?If @@Rowcount is checked after Error checking statement then it will have 0 as the value of @@Recordcount as it would have been reset.And if @@Recordcount is checked before the error-checking statement then @@Error would get reset. To get @@error and @@rowcount at the same time do both in same statement and store them in local variable. SELECT @RC = @@ROWCOUNT, @ER = @@ERROR
What is Identity?Identity (or AutoNumber) is a column that automatically generates numeric values. A start and increment value can be set, but most DBA leave these at 1. A GUID column also generates numbers; the value of this cannot be controled. Identity/GUID columns do not need to be indexed.
What is a Scheduled Jobs or What is a Scheduled Tasks? Scheduled tasks let user automate processes that run on regular or predictable cycles. User can schedule administrative tasks, such as cube processing, to run during times of slow business activity. User can also determine the order in which tasks run by creating job steps within a SQL Server Agent job. E.g. back up database, Update Stats of Tables. Job steps give user control over flow of execution. If one job fails, user can configure SQL Server Agent to continue to run the remaining tasks or to stop execution.
What is a table called, if it does have neither Cluster nor Non-cluster Index? What is it used for?Unindexed table or Heap. Microsoft Press Books and Book on Line (BOL) refers it as Heap.A heap is a table that does not have a clustered index and, therefore, the pages are not linked by pointers. The IAM pages are the only structures that link the pages in a table together.Unindexed tables are good for fast storing of data. Many times it is better to drop all indexes from table and than do bulk of inserts and to restore those indexes after that.
What is BCP? When does it used? BulkCopy is a tool used to copy huge amount of data from tables and views. BCP does not copy the structures same as source to destination.
How do you load large data to the SQL server database?BulkCopy is a tool used to copy huge amount of data from tables. BULK INSERT command helps to Imports a data file into a database table or view in a user-specified format.
Can we rewrite subqueries into simple select statements or with joins? Subqueries can often be re-written to use a standard outer join, resulting in faster performance. As we may know, an outer join uses the plus sign (+) operator to tell the database to return all non-matching rows with NULL values. Hence we combine the outer join with a NULL test in the WHERE clause to reproduce the result set without using a sub-query.
Can SQL Servers linked to other servers like Oracle?SQL Server can be lined to any server provided it has OLE-DB provider from Microsoft to allow a link. E.g. Oracle has an OLE-DB provider for oracle that Microsoft provides to add it as linked server to SQL Server group.
How to know which index a table is using? SELECT table_name, index_name FROM user_constraints
How to copy the tables, schema and views from one SQL server to another?Microsoft SQL Server 2000 Data Transformation Services (DTS) is a set of graphical tools and programmable objects that lets user extract, transform, and consolidate data from disparate sources into single or multiple destinations.
What is Self Join?This is a particular case when one table joins to itself, with one or two aliases to avoid confusion. A self join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it involves a relationship with only one table. The common example is when company have a hierarchal reporting structure whereby one member of staff reports to another.
What is Cross Join?A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The common example is when company wants to combine each product with a pricing table to analyze each product at each price.
Which virtual table does a trigger use?Inserted and Deleted.
List few advantages of Stored Procedure.
Stored procedure can reduced network traffic and latency, boosting application performance.
Stored procedure execution plans can be reused, staying cached in SQL Server’s memory, reducing server overhead.
Stored procedures help promote code reuse.
Stored procedures can encapsulate logic. You can change stored procedure code without affecting clients.
Stored procedures provide better security to your data.
What is DataWarehousing?
Subject-oriented, meaning that the data in the database is organized so that all the data elements relating to the same real-world event or object are linked together;
Time-variant, meaning that the changes to the data in the database are tracked and recorded so that reports can be produced showing changes over time;
Non-volatile, meaning that data in the database is never over-written or deleted, once committed, the data is static, read-only, but retained for future reporting;
Integrated, meaning that the database contains data from most or all of an organization’s operational applications, and that this data is made consistent.
What is OLTP (OnLine Transaction Processing)?In OLTP - online transaction processing systems relational database design use the discipline of data modeling and generally follow the Codd rules of data normalization in order to ensure absolute data integrity. Using these rules complex information is broken down into its most simple structures (a table) where all of the individual atomic level elements relate to each other and satisfy the normalization rules.
How do SQL server 2000 and XML linked? Can XML be used to access data?FOR XML (ROW, AUTO, EXPLICIT)You can execute SQL queries against existing relational databases to return results as XML rather than standard rowsets. These queries can be executed directly or from within stored procedures. To retrieve XML results, use the FOR XML clause of the SELECT statement and specify an XML mode of RAW, AUTO, or EXPLICIT.
OPENXMLOPENXML is a Transact-SQL keyword that provides a relational/rowset view over an in-memory XML document. OPENXML is a rowset provider similar to a table or a view. OPENXML provides a way to access XML data within the Transact-SQL context by transferring data from an XML document into the relational tables. Thus, OPENXML allows you to manage an XML document and its interaction with the relational environment.
What is an execution plan? When would you use it? How would you view the execution plan?An execution plan is basically a road map that graphically or textually shows the data retrieval methods chosen by the SQL Server query optimizer for a stored procedure or ad-hoc query and is a very useful tool for a developer to understand the performance characteristics of a query or stored procedure since the plan is the one that SQL Server will place in its cache and use to execute the stored procedure or query. From within Query Analyzer is an option called “Show Execution Plan” (located on the Query drop-down menu). If this option is turned on it will display query execution plan in separate window when query is ran again.
How do you implement one-to-one, one-to-many and many-to-many relationships while designing tables?
One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships. One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships. Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table. It will be a good idea to read up a database designing fundamentals text book.
What’s the difference between a primary key and a unique key?
Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only.
What is user defined data types and when you should go for them?
User defined data types let you extend the base SQL Server data types by providing a descriptive name, and format to the database. Take for example, in your database, there is a column called Flight_Num which appears in many tables. In all these tables it should be varchar (8). In this case you could create a user defined data type called Flight_num_type of varchar (8) and use it across all your tables. See sp_addtype, sp_droptype in books online.
What is bit data type and what’s the information that can be stored inside a bit column?
Bit data type is used to store Boolean information like 1 or 0 (true or false). Until SQL Server 6.5 bit data type could hold either a 1 or 0 and there was no support for NULL. But from SQL Server 7.0 onwards, bit data type can represent a third state, which is NULL.
Define candidate key, alternate key, and composite key.
A candidate key is one that can identify each row of a table uniquely. Generally a candidate key becomes the primary key of the table. If the table has more than one candidate key, one of them will become the primary key, and the rest are called alternate keys. A key formed by combining at least two or more columns is called composite key.
What are defaults? Is there a column to which a default can’t be bound?
A default is a value that will be used by a column, if no value is supplied to that column while inserting data. IDENTITY columns and timestamp columns can’t have defaults bound to them. See CREATE DEFAULT in books online.
What is a transaction and what are ACID properties?
A transaction is a logical unit of work in which, all the steps must be performed or none. ACID stands for Atomicity, Consistency, Isolation, and Durability. These are the properties of a transaction. For more information and explanation of these properties, see SQL Server books online or any RDBMS fundamentals text book. Explain different isolation levels An isolation level determines the degree of isolation of data between concurrent transactions. The default SQL Server isolation level is Read Committed. Here are the other isolation levels (in the ascending order of isolation): Read Uncommitted, Read Committed, Repeatable Read, and Serializable. See SQL Server books online for an explanation of the isolation levels. Be sure to read about SET TRANSACTION ISOLATION LEVEL, which lets you customize the isolation level at the connection level. Read Committed - A transaction operating at the Read Committed level cannot see changes made by other transactions until those transactions are committed. At this level of isolation, dirty reads are not possible but nonrepeatable reads and phantoms are possible. Read Uncommitted - A transaction operating at the Read Uncommitted level can see uncommitted changes made by other transactions. At this level of isolation, dirty reads, nonrepeatable reads, and phantoms are all possible. Repeatable Read - A transaction operating at the Repeatable Read level is guaranteed not to see any changes made by other transactions in values it has already read. At this level of isolation, dirty reads and nonrepeatable reads are not possible but phantoms are possible. Serializable - A transaction operating at the Serializable level guarantees that all concurrent transactions interact only in ways that produce the same effect as if each transaction were entirely executed one after the other. At this isolation level, dirty reads, nonrepeatable reads, and phantoms are not possible.
CREATE INDEX my Index ON my Table (my Column) what type of Index will get created after executing the above statement?
Non-clustered index. Important thing to note: By default a clustered index gets created on the primary key, unless specified otherwise.
What’s the maximum size of a row?
8060 bytes. Don’t be surprised with questions like ‘what is the maximum number of columns per table’. 1024 columns per table. Check out SQL Server books online for the page titled: "Maximum Capacity Specifications". Explain Active/Active and Active/Passive cluster configurations hopefully you have experience setting up cluster servers. But if you don’t, at least be familiar with the way clustering works and the two clustering configurations Active/Active and Active/Passive. SQL Server books online has enough information on this topic and there is a good white paper available on Microsoft site. Explain the architecture of SQL Server This is a very important question and you better be able to answer it if consider yourself a DBA. SQL Server books online is the best place to read about SQL Server architecture. Read up the chapter dedicated to SQL Server Architecture.
What is lock escalation?
Lock escalation is the process of converting a lot of low level locks (like row locks, page locks) into higher level locks (like table locks). Every lock is a memory structure too many locks would mean, more memory being occupied by locks. To prevent this from happening, SQL Server escalates the many fine-grain locks to fewer coarse-grain locks. Lock escalation threshold was definable in SQL Server 6.5, but from SQL Server 7.0 onwards it’s dynamically managed by SQL Server.
What’s the difference between DELETE TABLE and TRUNCATE TABLE commands?
DELETE TABLE is a logged operation, so the deletion of each row gets logged in the transaction log, which makes it slow. TRUNCATE TABLE also deletes all the rows in a table, but it won’t log the deletion of each row, instead it logs the deallocation of the data pages of the table, which makes it faster. Of course, TRUNCATE TABLE can be rolled back. TRUNCATE TABLE is functionally identical to DELETE statement with no WHERE clause: both remove all rows in the table. But TRUNCATE TABLE is faster and uses fewer system and transaction log resources than DELETE. The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table’s data, and only the page deallocations are recorded in the transaction log. TRUNCATE TABLE removes all rows from a table, but the table structure and its columns, constraints, indexes and so on remain. The counter used by an identity for new rows is reset to the seed for the column. If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement. You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint; instead, use DELETE statement without a WHERE clause. Because TRUNCATE TABLE is not logged, it cannot activate a trigger. TRUNCATE TABLE may not be used on tables participating in an indexed view
Explain the storage models of OLAP
Check out MOLAP, ROLAP and HOLAP in SQL Server books online for more information.
What are the new features introduced in SQL Server 2000 (or the latest release of SQL Server at the time of your interview)? What changed between the previous version of SQL Server and the current version?
This question is generally asked to see how current your knowledge is. Generally there is a section in the beginning of the books online titled "What’s New", which has all such information. Of course, reading just that is not enough; you should have tried those things to better answer the questions. Also check out the section titled "Backward Compatibility" in books online which talks about the changes that have taken place in the new version.
What are constraints? Explain different types of constraints.
Constraints enable the RDBMS enforce the integrity of the database automatically, without needing you to create triggers, rule or defaults. Types of constraints: NOT NULL, CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY. For an explanation of these constraints see books online for the pages titled: "Constraints" and "CREATE TABLE", "ALTER TABLE"
What is an index? What are the types of indexes? How many clustered indexes can be created on a table? I create a separate index on each column of a table. What are the advantages and disadvantages of this approach?
Indexes in SQL Server are similar to the indexes in books. They help SQL Server retrieve the data quicker. Indexes are of two types. Clustered indexes and non-clustered indexes. When you create a clustered index on a table, all the rows in the table are stored in the order of the clustered index key. So, there can be only one clustered index per table. Non-clustered indexes have their own storage separate from the table data storage. Non-clustered indexes are stored as B-tree structures (so do clustered indexes), with the leaf level nodes having the index key and its row locater. The row located could be the RID or the Clustered index key, depending up on the absence or presence of clustered index on the table. If you create an index on each column of a table, it improves the query performance, as the query optimizer can choose from all the existing indexes to come up with an efficient execution plan. At the same time, data modification operations (such as INSERT, UPDATE, DELETE) will become slow, as every time data changes in the table, all the indexes need to be updated. Another disadvantage is that, indexes need disk space, the more indexes you have, more disk space is used.
What is RAID and what are different types of RAID configurations?
RAID stands for Redundant Array of Inexpensive Disks, used to provide fault tolerance to database servers. There are six RAID levels 0 through 5 offering different levels of performance, fault tolerance. MSDN has some information about RAID levels and for detailed information, check out the RAID advisory board’s homepage
What are the steps you will take to improve performance of a poor performing query?
This is a very open ended question and there could be a lot of reasons behind the poor performance of a query. But some general issues that you could talk about would be: No indexes, table scans, missing or out of date statistics, blocking, excess recompilations of stored procedures, procedures and triggers without SET NOCOUNT ON, poorly written query with unnecessarily complicated joins, too much normalization, excess usage of cursors and temporary tables. Some of the tools/ways that help you troubleshooting performance problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance monitor, Graphical execution plan in Query Analyzer. Download the white paper on performance tuning SQL Server from Microsoft web site. Don’t forget to check out sql-server-performance.com
What are the steps you will take, if you are tasked with securing an SQL Server?
Again this is another open ended question. Here are some things you could talk about: Preferring NT authentication, using server, database and application roles to control access to the data, securing the physical database files using NTFS permissions, using an unguessable SA password, restricting physical access to the SQL Server, renaming the Administrator account on the SQL Server computer, disabling the Guest account, enabling auditing, using multiprotocol encryption, setting up SSL, setting up firewalls, isolating SQL Server from the web server etc. Read the white paper on SQL Server security from Microsoft website. Also check out My SQL Server security best practices
What is a deadlock and what is a live lock? How will you go about resolving deadlocks?
Deadlock is a situation when two processes, each having a lock on one piece of data, attempt to acquire a lock on the other’s piece. Each process would wait indefinitely for the other to release the lock, unless one of the user processes is terminated. SQL Server detects deadlocks and terminates one user’s process. A livelock is one, where a request for an exclusive lock is repeatedly denied because a series of overlapping shared locks keeps interfering. SQL Server detects the situation after four denials and refuses further shared locks. A livelock also occurs when read transactions monopolize a table or page, forcing a write transaction to wait indefinitely. Check out SET DEADLOCK_PRIORITY and "Minimizing Deadlocks" in SQL Server books online. Also check out the article Q169960 from Microsoft knowledge base.
What is blocking and how would you troubleshoot it?
Blocking happens when one connection from an application holds a lock and a second connection requires a conflicting lock type. This forces the second connection to wait, blocked on the first. Read up the following topics in SQL Server books online: Understanding and avoiding blocking, Coding efficient transactions. Explain CREATE DATABASE syntax Many of us are used to creating databases from the Enterprise Manager or by just issuing the command: CREATE DATABAE MyDB.
But what if you have to create a database with two file groups, one on drive C and the other on drive D with log on drive E with an initial size of 600 MB and with a growth factor of 15%?
That’s why being a DBA you should be familiar with the CREATE DATABASE syntax. Check out SQL Server books online for more information.
How to restart SQL Server in single user mode? How to start SQL Server in minimal configuration mode?
SQL Server can be started from command line, using the SQLSERVR.EXE. This EXE has some very important parameters with which a DBA should be familiar with. -m is used for starting SQL Server in single user mode and -f is used to start the SQL Server in minimal configuration mode. Check out SQL Server books online for more parameters and their explanations.
As a part of your job, what are the DBCC commands that you commonly use for database maintenance?
DBCC CHECKDB, DBCC CHECKTABLE, DBCC CHECKCATALOG, DBCC CHECKALLOC, DBCC SHOWCONTIG, DBCC SHRINKDATABASE, DBCC SHRINKFILE etc. But there are a whole load of DBCC commands which are very useful for DBAs. Check out SQL Server books online for more information.
What are statistics, under what circumstances they go out of date, and how do you update them?
Statistics determine the selectivity of the indexes. If an indexed column has unique values then the selectivity of that index is more, as opposed to an index with non-unique values. Query optimizer uses these indexes in determining whether to choose an index or not while executing a query. Some situations under which you should update statistics: 1) If there is significant change in the key values in the index 2) If a large amount of data in an indexed column has been added, changed, or removed (that is, if the distribution of key values has changed), or the table has been truncated using the TRUNCATE TABLE statement and then repopulated 3) Database is upgraded from a previous version. Look up SQL Server books online for the following commands: UPDATE STATISTICS, STATS_DATE, DBCC SHOW_STATISTICS, CREATE STATISTICS, DROP STATISTICS, sp_autostats, sp_createstats, and sp_updatestats
What are the different ways of moving data/databases between servers and databases in SQL Server?
There are lots of options available; you have to choose your option depending upon your requirements. Some of the options you have are: BACKUP/RESTORE, detaching and attaching databases, replication, DTS, BCP, log shipping, INSERT…SELECT, SELECT…INTO, creating INSERT scripts to generate data.
Explain different types of BACKUPs available in SQL Server? Given a particular scenario, how would you go about choosing a backup plan?
Types of backups you can create in SQL Sever 7.0+ are Full database backup, differential database backup, transaction log backup, file group backup. Check out the BACKUP and RESTORE commands in SQL Server books online. Be prepared to write the commands in your interview. Books online also has information on detailed backup/restore architecture and when one should go for a particular kind of backup.
What is database replication? What are the different types of replication you can set up in SQL Server?
Replication is the process of copying/moving data between databases on the same or different servers. SQL Server supports the following types of replication scenarios:? Snapshot replication? Transactional replication (with immediate updating subscribers, with queued updating subscribers)? Merge replication See SQL Server books online for in depth coverage on replication. Be prepared to explain how different replication agents function, what are the main system tables used in replication etc.
How to determine the service pack currently installed on SQL Server?
The global variable @@Version stores the build number of the sqlservr.exe, which is used to determine the service pack installed. To know more about this process visit SQL Server service packs and versions.
What are cursors? Explain different types of cursors. What are the disadvantages of cursors? How can you avoid cursors?
Cursors allow row-by-row processing of the result sets. Types of cursors: Static, Dynamic, Forward-only, Keyset-driven. See books online for more information. Disadvantages of cursors: Each time you fetch a row from the cursor, it results in a network roundtrip; where as a normal SELECT query makes only one roundtrip, however large the result set is. Cursors are also costly because they require more resources and temporary storage (results in more IO operations). Further, there are restrictions on the SELECT statements that can be used with some types of cursors. Most of the times, set based operations can be used instead of cursors. Here is an example: If you have to give a flat hike to your employees using the following criteria: Salary between 30000 and 40000 — 5000 hike Salary between 40000 and 55000 — 7000 hike Salary between 55000 and 65000 — 9000 hike. In this situation many developers tend to use a cursor, determine each employee’s salary and update his salary according to the above formula. But the same can be achieved by multiple update statements or can be combined in a single UPDATE statement as shown below:
UPDATE tbl_emp SET salary = CASE WHEN salary BETWEEN 30000 AND 40000 THEN salary + 5000 WHEN salary BETWEEN 40000 AND 55000 THEN salary + 7000 WHEN salary BETWEEN 55000 AND 65000 THEN salary + 10000 END
Another situation in which developers tend to use cursors: You need to call a stored procedure when a column in a particular row meets certain condition. You don’t have to use cursors for this. This can be achieved using WHILE loop, as long as there is a unique key to identify each row. For examples of using WHILE loop for row by row processing, check out the ‘My code library’ section of my site or search for WHILE. Write down the general syntax for a SELECT statement covering all the options. Here’s the basic syntax: (Also checkout SELECT in books online for advanced syntax).
SELECT select list [INTO new table_] FROM table source [WHERE search condition] [GROUP BY group_by_expression] [HAVING search condition] [ORDER BY order expression [ASC DESC] ]
What is a join and explain different types of joins.
Joins are used in queries to explain how different tables are related. Joins also let you select data from a table depending upon data from another table. Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS. For more information see pages from books online titled: "Join Fundamentals" and "Using Joins".
Can you have a nested transaction?
Yes, very much. Check out BEGIN TRAN, COMMIT, ROLLBACK, SAVE TRAN and @@TRANCOUNT
What is an extended stored procedure? Can you instantiate a COM object by using T-SQL?
An extended stored procedure is a function within a DLL (written in a programming language like C, C++ using Open Data Services (ODS) API) that can be called from T-SQL, just the way we call normal stored procedures using the EXEC statement. See books online to learn how to create extended stored procedures and how to add them to SQL Server. Yes, you can instantiate a COM (written in languages like VB, VC++) object from T-SQL by using sp_OACreate stored procedure. Also see books online for sp_OAMethod, sp_OAGetProperty, sp_OASetProperty, sp_OADestroy. For an example of creating a COM object in VB and calling it from T-SQL, see ‘My code library’ section of this site.
What is the system function to get the current user’s user id?
USER_ID (). Also check out other system functions like USER_NAME (), SYSTEM_USER, SESSION_USER, CURRENT_USER, USER, SUSER_SID (), HOST_NAME ().
What are triggers? How many triggers you can have on a table? How to invoke a trigger on demand?
Triggers are special kind of stored procedures that get executed automatically when an INSERT, UPDATE or DELETE operation takes place on a table. In SQL Server 6.5 you could define only 3 triggers per table, one for INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0 onwards, this restriction is gone, and you could create multiple triggers per each action. But in 7.0 there’s no way to control the order in which the triggers fire. In SQL Server 2000 you could specify which trigger fires first or fires last using sp_settriggerorder. Triggers can’t be invoked on demand. They get triggered only when an associated action (INSERT, UPDATE, and DELETE) happens on the table on which they are defined. Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster. Till SQL Server 7.0, triggers fire only after the data modification operation happens. So in a way, they are called post triggers. But in SQL Server 2000 you could create pre triggers also. Search SQL Server 2000 books online for INSTEAD OF triggers. Also check out books online for ‘inserted table’, ‘deleted table’ and COLUMNS_UPDATED ()
There is a trigger defined for INSERT operations on a table, in an OLTP system. The trigger is written to instantiate a COM object and pass the newly inserted rows to it for some custom processing. What do you think of this implementation? Can this be implemented better?
Instantiating COM objects is a time consuming process and since you are doing it from within a trigger, it slows down the data insertion process. Same is the case with sending emails from triggers. This scenario can be better implemented by logging all the necessary data into a separate table, and have a job which periodically checks this table and does the needful.
What is a self join? Explain it with an example.
Self join is just like any other join, except that two instances of the same table will be joined in the query. Here is an example: Employees table which contains rows for normal employees as well as managers. So, to find out the managers of all the employees, you need a self join.
CREATE TABLE emp ( empid int, mgrid int, empname char(10) )
INSERT emp SELECT 1,2,’Vyas’ INSERT emp SELECT 2,3,’Mohan’ INSERT emp SELECT 3,NULL,’Shobha’ INSERT emp SELECT 4,2,’Shridhar’ INSERT emp SELECT 5,2,’Sourabh’
SELECT t1.empname [Employee], t2.empname [Manager] FROM emp t1, emp t2 WHERE t1.mgrid = t2.empid Here’s an advanced query using a LEFT OUTER JOIN that even returns the employees without managers (super bosses)
SELECT t1.empname [Employee], COALESCE(t2.empname, ‘No manager’) [Manager] FROM emp t1 LEFT OUTER JOIN emp t2 ON t1.mgrid = t2.empid

Tuesday, November 18, 2008

Storage Classes in OLAP

A big advantage of a BI solution is the existence of a cube. Data and aggregations are stored in a optimized format to offer very fast query performance. Sometimes, a big disadvantage of storing data and aggregations in a cube is the latency that it implies. SSAS processes data from the underlying relational database into the cube. After this is done the cube is no longer connected to the relational database so changes to this database will not be reflected in the cube. Only when the cube is processed again, the data in the cube will be refreshed.SSAS 2005 gives you the possibility to choose different storage types for the following objects:
Cubes
Partitions
DimensionsMOLAP (Multi dimensional Online Analytical Processing)MOLAP is the most used storage type. Its designed to offer maximum query performance to the users. Data AND aggregations are stored in optimized format in the cube. The data inside the cube will refresh only when the cube is processed, so latency is high.
ROLAP (Relational Online Analytical Processing)ROLAP does not have the high latency disadvantage of MOLAP. With ROLAP, the data and aggregations are stored in relational format. This means that there will be zero latency between the relational source database and the cube. Disadvantage of this mode is the performance, this type gives the poorest query performance because no objects benefit from multi dimensional storage. HOLAP (Hybrid Online Analytical Processing)HOLAP is a storage type between MOLAP and ROLAP. Data will be stored in relational format(ROLAP), so there will also be zero latency with this storage type. Aggregations, on the other hand, are stored in multi dimensional format(MOLAP) in the cube to give better query performance. SSAS will listen to notifications from the source relational database, when changes are made, SSAS will get a notification and will process the aggregations again.With this mode it’s possible to offer zero latency to the users but with medium query performance compared to MOLAP and ROLAP.The different storage types of SSAS:

Data storage
Aggregations storage
Query performance
Latency
MOLAP
Cube
Cube
High
High
HOLAP
Relational database
Cube
Medium
Low (none)
ROLAP
Relational database
Relational database
Low
Low (none)ConclusionSSAS offers three storage types that give you all the flexibility you need. You can choose between high performance and high latency on one side(MOLAP) and lower performance but low latency(ROLAP) on the other side. There is also a possibility to choose a way in between(HOLAP).

Detail Description About MCTS

So why is this exam difficult? I think it’s because of the amount of detail in the questions. You can expect very detailed questions about, for example, properties of SSIS, SSAS and SSRS.Let’s look at the exam topics of exam 70-445: (full list: Microsoft Learning)The following list includes the topic areas covered on this exam. The percentage indicates the portion of the exam that addresses a particular skill.• Managing SSAS (12 percent)• Developing SSAS Solutions by Using BIDS (18 percent)• Implementing data mining by Using BIDs (12 percent)• Managing SSRS (13 percent)• Developing Reporting Solutions by Using SSRS (19 percent)• Developing Business Intelligence Solutions by Using SSIS (16 percent)• Administering SSIS Packages (11 percent)Datamining Notice that data mining is an important topic of this exam. I know that a lot of people score poor on the data mining questions so take your time to master enough knowledge!A lot of the questions have focus on deployment and maintenance. This exam is not about, for example, SSIS tasks and transformations but it is about the deployment of SSIS packages and the working and use of transactions.Training KitI used the 70-445 Training Kit from Microsoft Press to prepare for the exam: AmazonThis book will help you a lot while preparing for the exam! It is full of effective information and contains a lot of hands-on labs and test questions. A must have, if you ask me!Number of questions and completing timeAs last I can tell you that the exam contains 53 questions and you have 150 minutes to complete it. You will have time enough, so don’t worry about it. You need to score 700 points out of 1000 to pass.
Question typesThe 70-445 exam is multiple choice, there are no questions that you need to answer by typing text.There are 3 types of questions:
1.This type of question is the easiest one. One answer can be selected only. I think 60% of the questions are of this type.
2.This type of question is harder then type 1. More answers can be selected. In this example only 2 answers should be selected, this can vary. I remember questions with 3 answers that should be selected and also questions where you will be asked to pick 1 or more good answers. I think 25% of the questions are of this type.

How To Get MCTS Certification..?

hi Friends..!
i am sharing some useful links to crack the MCTS certification.
Exam 70-445->syllabus->http://www.microsoft.com/learning/en/us/exams/70-445.mspx
Exam 70-446->syllabus->http://www.microsoft.com/learning/en/us/exams/70-446.mspx
Register online->http://www.register.prometric.com/error/NoCookie.asp?cookie%5Ftest=1
some more links are added .
go thru all the links,you will definitely get a overview about the certification.
Enjoy..!
Cheers.
Rav's

MCTS(70-445)

hi Friends..!
right now i am planning to prepare for the Certification.
if you have any material or links,forward to me.
i will share some stuff,what i have presently for this exam.
Thanks in Advance.
Rav's.

Thursday, November 6, 2008

Maintenace Tasks in SSIS

hi one to all,
i have lot of issues on the ssis maintenace tasks.
it wont work properly.
the main work is i have to maintenance Backup,Restore,Initialize,UpdateSuccess and Archive the Tables.
i will present a link for you..!
http://blog.ola.hallengren.com/

Wednesday, November 5, 2008

hi

hi
its all about MSBI details.
give a look and send your feed back


Many thanks
Rav's