Sql Server Interview Questions part 1

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. 

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. 

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. 

 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. 

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. 

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. 

 There are basically two types of indexes that we use with the SQL Server. Clustered and the Non-Clustered. 

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. 

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. 

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. 

SQL Server runs on port 1433 but we can also change it for better security. 

From the Network Utility TCP/IP properties –> Port number.both on client and the server. 

 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. 

 No. We cannot use Truncate command on a table with Foreign Key because of referential integrity. 

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. 

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. 

sp_renamedb ‘oldname’ , ‘newname’ 

In such cases we can first bring to db to single user using sp_dboptions and then we can rename that db and then we can rerun the sp_dboptions command to remove the single user mode. 

 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.