SQL SERVER INTERVIEW QUESTIONS 2014 BOOKLET -5 By Mr.J.Venkatesan Prabu - Managing Director of Kaashiv Infotech

"Mr.J.Venkatesan Prabu" 


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

    SQL Server Interview Questions 2014
SQL  SERVER –Booklet 5
-         Gives you the interview tips for SQL Server


1. 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.
2.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.
3. 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.
4. What are the authentication modes in SQL Server? How can it be changed?

Windows mode and Mixed Mode - SQL and Windows. To change authentication mode in SQL Server click Start, Programs, 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.

5. What is normalization ?

Normalization is a design technique that  is widely used as a guide in designing  relational databases. Normalization is essentially a two step process that  puts data into tabular form by removing repeating groups and then removes duplicated data from the relational tables                                                                               

6. What is meant by First Normal Form

A database is said to be in First Normal Form when all entities have a unique identifier or key, and when every column in every table contains only a single value and doesn't contain a repeating group or composite field.

7. What is meant by Second Normal Form

A database is in Second Normal Form when it is in First Normal Form plus every non-primary key column in the table must depend on the entire primary key, not just part of it, assuming that the primary key is made up of composite columns.

8 .What is meant by Third Normal Form

A database is in Third Normal Form when it is in Second Normal Form and each column that isn't part of the primary key doesn't depend on another column that isn't part of the primary key.

9. When to denormalize ?

Typically, transactional databases are highly normalized. This means that redundant data is eliminated and replaced with keys in a one-to-many relationship. Data that is highly normalized is constrained by the primary key/foreign key relationship, and thus has a high degree of data integrity. Denormalized data, on the other hand, creates redundancies; this means that it's possible for denormalized data to lose track of some of the relationships between atomic data items. However, since all the data for a query is (usually) stored in a single row in the table, it is much faster to retrieve.

10. How can you performance tune your database ?

Ø  Denormalize your tables where appropriate.
Ø  Proper use of index columns: An index based on numeric fields is more efficient than an index based on character columns.
Ø  Reduce the number of columns that make up a composite key.
Ø  Proper partitioning of tablespaces and create a special tablespace for special data types like CLOB, BLOB etc.
Data access performance can be tuned by using stored procedures to crunch data in the database server to reduce the network overhead and also caching data within your application to reduce the number of accesses.

11. How will you map objects to a relational database ? How will you map class inheritance to relational data model ?

Due to impedance mismatch between object and relational technology you need to understand the process of mapping classes (objects) and their relationships to tables and relationships between them in a database. Classes represent both behavior and data whereas relational database tables just implement data. Database schemas have keys (primary keys to uniquely identify rows and foreign keys to maintain relationships between rows) whereas object schema does not have keys and instead use references to implement relationships to other objects.
Ø  Classes map to tables in a way but not always directly.
Ø    An attribute of a class can be mapped to zero or more columns in a database. Not all attributes are persistent.
Ø    Some attributes of an object are objects itself. For example an Employee object has an Address object as an attribute. This is basically an association relationship between two objects.
Ø   In its simple form an attribute maps to a single column whereas each has same type (i.e. attribute is a string and column is a char, or both are dates etc). When you implement mapping with different types (attribute is a currency and column is a float) then you will need to be able to convert them back and forth.

12. What is a view ? Why will you use a view? What is an aggregate function ?

View is a precompiled SQL query, which is used to select data from one or more tables. A view is like a table but it doesn’t physically take any space (i.e. not materialized).
Views are used for
Ø  Providing inherent security by exposing only the data that is needed to be shown to the end user.
Ø   Enabling re-use of SQL statements.
Ø  Allows changes to the underlying tables to be hidden from clients, aiding maintenance of the database schema (i.e. encapsulation)
Ø  Views with multiple joins and filters can dramatically degrade performance because views contain no data and any retrieval needs to be processed.
Ø   The solution for this is to use materialized views or create de-normalized tables to store data. This technique is quite handy in overnight batch processes where a large chunk of data needs to be processed. Normalized data can be read and inserted into some temporary denormalized table and processed with efficiency.

13. What is a database trigger ?

A trigger is a fragment of code that you tell to run before or after a table is modified. There are typically three triggering EVENTS that cause trigger to 'fire':
Ø  INSERT event (as a new record is being inserted into the database).
Ø  UPDATE event (as a record is being changed).
Ø    DELETE event (as a record is being deleted).
Triggers can restrict access to specific data, perform logging, or audit access to data.

14. How can you keep track of all your database changes ?

If you want to keep track of all changes to a particular record, such as who modified the record, what kind of modification took place, and when the record modification occurred then you can use triggers because you can capture every action that occurred on a particular table. For example, an INSERT trigger would fire when a particular database table has a record inserted. 
15. What is the difference between “Stored Procedure” and “Function”?

  1. A procedure can have both input and output parameters, but a function can only have input parameters.
  2. Inside a procedure we can use DML (INSERT/UPDATE/DELETE) statements. But inside a function we can't use DML statements.
  3. We can't utilize a Stored Procedure in a Select statement. But we can use a function in a Select statement.
  4. We can use a Try-Catch Block in a Stored Procedure but inside a function we can't use a Try-Catch block.
  5. We can use transaction management in a procedure but we can't in a function.
  6. We can't join a Stored Procedure but we can join functions.
  7. Stored Procedures cannot be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section. But we can use a function anywhere.
  8. A procedure can return 0 or n values (max 1024). But a function can return only 1 value that is mandatory.
  9. A procedure can't be called from a function but we can call a function from a procedure.

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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

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!!!
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