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SQL SERVER INTERVIEW QUESTIONS 2014 BOOKLET -3 By Mr.J.Venkatesan Prabu - Managing Director of Kaashiv Infotech

            
      SQL SERVER INTERVIEW QUESTIONS 2014- SET 3 By 
"Mr.J.Venkatesan Prabu" 

KAASHIV INFOTECH

     [ The  Asia, India & Tamil Nadu Book Of  Record Holders ]


                                                       
    SQL Server Interview Questions 2014
SQL  SERVER –Booklet 3
-         Gives you the interview tips for SQL Server

 SQL SERVER INTERVIEW QUESTIONS WITH ANSWERS 

1. What is UNIQUE KEY constraint?
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.

2. What is FOREIGN KEY?
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.

3. What is CHECK Constraint?
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.

4. When is the UPDATE_STATISTICS command used?
- When the processing of large data is done, this command is used.
- Whenever large number of deletions, modification or copy takes place into the tables, the indexes need to be updated to take care of these changes. UPDATE_STATISTICS performs this job.

5. Differentiate between a HAVING CLAUSE and a WHERE CLAUSE.
HAVING CLAUSE
- HAVING CLAUSE is used only with the SELECT statement.
- It is generally used in a GROUP BY clause in a query.
- If GROUP BY is not used, HAVING works like a WHERE clause.
WHERE Clause
- It is applied to each row before they become a part of the GROUP BY function in a query.
6. What do you understand by a view? What does the WITH CHECK OPTION clause for a view do?
- A view is a virtual table that consists of fields from one or more real tables.
- It is usually used to join multiple tables and get the data.
- The WITH CHECK OPTION for a view prevents any modification to the data that does not confirm to the WHERE clause of the view definition.
- This allows the data belonging to the view to be updated through the view.

7. Explain query execution plan?
- The optimizer available in SQL Server optimizes the code to be effectively executed.
- A query execution plan shows how this optimizer would run the query.
- Query execution plan can be viewed by :
- Using the Show Execution Plan option available in Query Analyzer,
- Displaying Estimated Execution Plan on the query dropdown menu,
- Use the SET SHOWPLAN_TEXT ON command before running a query and capturing the execution plan event in a SQL Server Profiler trace.

8. What is the function of SQL Server Agent Windows service?

- It is a Windows service which handles the tasks scheduled within the SQL Server environment. These tasks are also called as job and are stored with in SQL server. The jobs may run through a trigger, a predefined schedule or on demand.
- This service is very useful in determining why a particular job did not run as intended.

9. Comment on Transactions.
- Using transactions we can group all SQL commands into a single unit.
- The transaction begins with some task and finishes only when all tasks within it are over.
- The transaction gets over successfully only when all commands in it are successfully over. Even if one command fails, the whole transaction fails.
- The BEGIN TRANSACTION, ROLLBACK TRANSACTION, and COMMIT TRANSACTION statements are used to work with transactions.
- A group of tasks starts with the begin statement.
- In case of any problem, the rollback command is executed to abort the transaction.
- If all the tasks run successfully, all commands are executed through commit statement.

10. Differentiate between a primary key and a unique key.
- By default, clustered index on the column are created by the primary key whereas nonclustered index are created by unique key.
- Primary key doesn't allow NULLs, but unique key allows one NULL.

11. What is recursion? Is it possible for a stored procedure to call itself or recursive stored procedure?  How many levels of SP nesting is possible?
Recursion is method of problem solving where the solution is arrived at by repetitively applying the logic and solution to the subsets of the problem.
Transact-SQL supports recursion. So, yes it is possible for a stored procedure to call itself.
Stored procedures and managed code references can be nested up to 32 levels.

12. What are the advantages of using Stored Procedures?
- They help in reducing the network traffic and latency which in turn boosts application performance.
- They help in promoting code reuse.
- They provide better security to data.
- It is possible to encapsulate the logic using stored procedures. This allows to change stored procedure code without affecting clients.
- It is possible to reuse stored procedure execution plans, which are cached in SQL Server's memory. This reduces server overhead.

13. You want to implement the following relationships while designing tables. How would you do it?
a.) One-to-one
b.) One-to-many
c.) Many-to-many
a.) One-to-One relationship - can be implemented as a single table and rarely as two tables with primary and foreign key relationships.

b.) One-to-Many relationships - by splitting the data into two tables with primary key and foreign key relationships.

c.) Many-to-Many - by using a junction table with the keys from both the tables forming the composite primary key of the junction table.

14. Differentiate between DELETE and TRUNCATE.
- Truncate can not be rolled back while Delete can be.
- Truncate keeps the lock on table while Delete keeps the lock on each row.
- Truncate resets the counter of the Identity column while Delete doesn't do so.
- Trigger is not fired in Truncate while it happens in Delete.

15. What are the properties of the Relational tables?
Relational tables have six properties:
1. Values are atomic.
2. Column values are of the same kind.
3. Each row is unique.
4. The sequence of columns is insignificant.
5. The sequence of rows is insignificant.
6. Each column must have a unique name.


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My T-SQL Gallery @code.msdn.microsoft


Created my own T-SQL Gallery in Microsoft site. Do visit the same and share your feedback,

http://code.msdn.microsoft.com/VenkatSQLSample/Thread/List.aspx

Thanks and Regards,
Venkatesan Prabu .J

SQL Server Interview questions - Part 1

What is the significance of NULL value and why should we avoid permitting null values?
Null means no entry has been made. It implies that the value is either unknown or undefined.We should avoid permitting null values because Column with NULL values can't have PRIMARY KEY constraints. Certain calculations can be inaccurate if NULL columns are involved.

What is SQL whats its uses and its component ?
The Structured Query Language (SQL) is foundation for all relational database systems. Most of the large-scale databases use the SQL to define all user and administrator interactions. It enable us to retrieve the data from based on our exact requirement. We will be given a flexibility to store the data in our own format.


The DML component of SQL comprises four basic statements:
* SELECT to get rows from tables
* UPDATE to update the rows of tables
* DELETE to remove rows from tables
* INSERT to add new rows to tables


What is DTS in SQL Server ?
Data Transformation Services is used to transfer the data from one source to our required destination. Considering am having some data in sql server and I need to transfer the data to Excel destination. Its highly possible with dialogue based tool called Data Transformation services. More customization can be achieved using SSIS. A specialized tool used to do such migration works.


What is the difference between SQL and Pl/Sql ?

Straight forward. SQL is a single statement to finish up our work.Considering, I need some data from a particular table. “Select * from table” will fetch the necessary information. Where as I need to do some row by row processing. In that case, we need to go for Procedural Logic / SQL.

What is the significance of NULL value and why should we avoid permitting null values?
Null means no entry has been made. It implies that the value is either unknown or undefined.We should avoid permitting null values because Column with NULL values can't have PRIMARY KEY constraints. Certain calculations can be inaccurate if NULL columns are involved.

Difference between primary key and Unique key?
Both constraints will share a common property called uniqueness. The data in the column should be unique. The basic difference is,
· Primary key won’t allow null value. Whereas, unique key will accept null value but only one null value.
· On creating primary key, it will automatically format the data inturn creates clustered index on the table. Whereas, this characteristics is not associated with unique key.
· Only one primary key can be created for the table. Any number of Unique key can be created for the table.

Select Statement in SQL Server

Select Statement in SQL Server

String Functions in sql server

String Functions in sql server
Substring/Len/replace/Ltrim/Rtrim

SQL Server Interview Question - Part 2

What is normalization?

Normalization is the basic concept used in designing a database. Its nothing but, an advise given to the database to have minimal repetition of data, highly structured, highly secured, easy to retrieve. In high level definition, the Process of organizing data into tables is referred to as normalization.


What is a stored procedure:
Stored procedures are precompiled T-SQL statements combined to perform a single task of several tasks. Its basically like a Macro so when you invoke the Stored procedure, you actually run a set of statements. As, its precompiled statement, execution of Stored procedure is compatatively high when compared to an ordinary T-SQL statement.


What is the difference between UNION ALL Statement and UNION ?
The main difference between UNION ALL statement and UNION is UNION All statement is much faster than UNION,the reason behind this is that because UNION ALL statement does not look for duplicate rows, but on the other hand UNION statement does look for duplicate rows, whether or not they exist.

Example for Stored Procedure?
They are three kinds of stored procedures,1.System stored procedure – Start with sp_2. User defined stored procedure – SP created by the user.3. Extended stored procedure – SP used to invoke a process in the external systems.Example for system stored proceduresp_helpdb - Database and its propertiessp_who2 – Gives details about the current user connected to your system. sp_renamedb – Enable you to rename your database


What is a trigger?

Triggers are precompiled statements similar to Stored Procedure. It will automatically invoke for a particular operation. Triggers are basically used to implement business rules.


What is a view?
If we have several tables in a db and we want to view only specific columns from specific tables we can go for views. It would also suffice the needs of security some times allowing specfic users to see only specific columns based on the permission that we can configure on the view. Views also reduce the effort that is required for writing queries to access specific columns every time.


What is an Index?
When queries are run against a db, an index on that db basically helps in the way the data is sorted to process the query for faster and data retrievals are much faster when we have an index.


What are the types of indexes available with SQL Server?

There are basically two types of indexes that we use with the SQL ServerClustered -

1. It will format the entire table, inturn physically sort the table.

2. Only one clustered index can be created for a table.

3. Data will be located in the leaf level.

4. By default, primary key will create clustered index on the table.

Non-Clustered Index

1. It wont touch the structure of the table.

2. It forms an index table as reference to the exact data.

3. A reference to the data will be located in the leaf level.

4. For a table, we can create 249 non clustered index.

Happy Learning!!!
Regards,
Venkatesan Prabu .J

SQL Interview question

Extent Vs Page?

Pages are low level unit to store the exact data in sql server. Basically, the data will be stored in the mdf, ldf, ndf files. Inturn, pages are logical units available in sql server.The size of the page is 8KB.

Eight consecutive pages will form an extent 8 * 8KB = 64KB.

Thus I/O level operation will be happening at pages level.The pages will hold a template information at the start of each page (header of the page).

They are,

1. page number,

2. page type,

3. the amount of free space on the page,

4. the allocation unit ID of the object that owns the page.

Extents will be classifed into two types,

1. Uniform extents

2. Mixed extents

Uniform Extents:It occupied or used by a single object. Inturn, a single object will hold the entire 8 pages.Mixed

Extents:Mulitple objects will use the same extent. SQL Server will allow a max of eight objects to use a shared extent.

Property of SQL Server :Initally if an object is created, sql server will allocate the object to the mixed extent and once if the size reaches 8 pages and more... immediately, a new uniform extent will be provided for that particular object.

Herecomes, our fragmentation and reindexing concepts.

Best Joke - Enjoy it

Best Joke - Enjoy it