27.9.08

SQL Server Interview Questions

RDBMS Vs DBMS:
Database management system is considered as the system to store the data for easy retieval and the data were relatively stored as a group. Whereas, Relational database management system will include a relationship between tables (using constraints). The relationship will be based on their logical relations. Considering,
There are two table "employee" which will hold employee information like, employee id, employee dob, where he is working. Another table "employee details" which may hold his personal information like blood group, identification etc..,
For these two tables, there should be a key which will form a relation ship between these two tables. Its nothing but RDBMS. (Eg: SQL Server, Oracle)

SQL Server Vs MS access:
I used to see this question acess vs sql server,
MS access is a RDBMS and can be considered as client level database. It comes along with Microsoft office package. The database will be formed based on filesystem concept, so it wont support multiuser environment. Its preferred for very small databases. It developed on Jet engine.
SQL Server is a RDBMS and works as a Server level database. It will work for a large group of Users with 24/7 availability and its preferred for high end system with huge data and huge support. Its developed on sql server engine.
Normalization:
Normalization is a very important consideration in designing the databases. Normalization includes various steps like,
1. First normal form
2. Second normal form
3. third normal form
4. Backus naur form
5. Extended Backus naur form
6. Fifth normal form
7. Sixth normal form
The above normal forms are used to avoid redundancy of data. To achieve these, we have to segregate the columns to different tables. So that, duplication should not be there, partial dependency should be avoided etc..,

Denormalization:
As the name indicates, it's opposite to normalisation. Introducing redundancy into the database is referred to as denormalization. The database becomes too complex and too many joins may occur to fetch the data. In that case, we used to prefer this denomalization concept. Narrow idea - Joining the divided or segregated tables.

MSDE vs SQL Server :
MSDE is the downgrade version of SQL Server, the same code with initial release of SQL Server was named as MSDE (Microsoft Desktop Enginer).

Extent Vs Page:
Pages are 8 KB size smallest unit to store the data. Inturn, 8 Pages will form the extent.

Delete VS Truncate:
Delete will delete row by row in the table. The syntax is,
delete from tablename
We can give where conditions for deleting the data.
Each delete will be logged in the log file.
Its a DML statement

Trucate will deallocate the reference in the pages instead of deleting the data.
Its DDL statement. The syntax is,
Truncate table tablename
We can provide truncate with tables having foreign key relationships. (Because it wont do any cascade delete on the table).
It wont log any information in the log file.
Delete or truncate the data at a stretch and wont do any row by row manipulation.

More SQL server Interview questions at,

http://venkattechnicalblog.blogspot.com/2008/09/sql-server-interview-questions_11.html

http://venkattechnicalblog.blogspot.com/2008/09/sql-server-interview-question-part-2.html

http://venkattechnicalblog.blogspot.com/2008/09/sql-server-interview-questions.html

Happy Learning!!!
Regards,
Venkatesan Prabu .J

6 comments:

fazal said...

To,
Sir

Please Give Me a Information About MSDBA Exams.

Thanks in Advance.

regards,
Fazal Vahora

Venkatesan Prabu said...

Hi Fazal,

Microsoft follows MCTS as a basic exam and MCITP as an advanced exam (DBA). Its equivalent to MCDBA. They have dropped MCDBA exam in future versions.

Regards,
Venkatesan Prabu .J

fazal said...

To,
Sir

When I Import .xls file to MS SQL SERVER 2005,some error arise is "The Product level is insufficient for Component ",please give me a answer,what is my mistake?

Thanks in Advance
Regards,
Fazal Vahora

Venkatesan Prabu said...

Fazal its a nice question. I too faced this situation in my work. The problem is due to the installables in your machine. Just check the services, whether you SSIS services is installed and its running...

You have installed only client components. It will allow you to create packages with lots of restrictions.

Thanks and Regards,
Venkatesan Prabu .J

kamesh said...

plz change the background color

curtis said...

Hi

I like this post:

You create good material for community.

Please keep posting.

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Source: IT interview questions

Best rgs
Peter

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