Thursday, March 29, 2012

Sql Server Interview Questions part 1

What is normalization?
Well a relational database is basically composed of tables that contain related data. So the Process of organizing this data into tables is actually referred to as normalization.

What is a Stored Procedure?
Its nothing but a set of 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.

Can you give an example of Stored Procedure?
sp_helpdb , sp_who2, sp_renamedb are a set of system defined stored procedures.
We can also have user defined stored procedures which can be called in similar way.

What is a trigger?
Triggers are basically used to implement business rules. Triggers is also similar to stored procedures.
The difference is that it can be activated when data is added or edited or deleted from a table in a database.

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 Server. Clustered and the Non-Clustered.

What is the basic difference between clustered and a non-clustered index?
The difference is that, Clustered index is unique for any given table and we can have only one clustered index on a table. The leaf level of a clustered index is the actual data and the data is resorted in case of clustered index. Whereas in case of non-clustered index the leaf level is actually a pointer to the data in rows so we can have as many non-clustered indexes as we can on the db.

What are cursors?
Well cursors help us to do an operation on a set of data that we retreive by commands such as Select columns from table. For example : If we have duplicate records in a table we can remove it by declaring a cursor which would check the records during retreival one by one and remove rows which have duplicate values.

When do we use the UPDATE_STATISTICS command?
This command is basically used when we do a large processing of data. If we do a large amount of deletions any modification or Bulk Copy into the tables, we need to basically update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.

Which TCP/IP port does SQL Server run on?
SQL Server runs on port 1433 but we can also change it for better security.

From where can you change the default port?
From the Network Utility TCP/IP properties –> Port number.both on client and the server.

Can you tell me the 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.

Can we use Truncate command on a table which is referenced by FOREIGN KEY?
No. We cannot use Truncate command on a table with Foreign Key because of referential integrity.

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.

Can you give me some DBCC command options?(Database consistency check)
DBCC CHECKDB - Ensures that tables in the db and the indexes are correctly linked.and DBCC CHECKALLOC - To check that all pages in a db are correctly allocated. DBCC SQLPERF - It gives report on current usage of transaction log in percentage. DBCC CHECKFILEGROUP - Checks all tables file group for any damage.

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