Technical SQL Questions:

1. What are the three different types of replication and how does replication work?
2. What is the purpose of log shipping and how does it work?
3. What is the difference between a clustered and a non clustered index?
4. What is a derived table and when would you use one?
5. What is a VIEW? How to get script for a view?
   View is virtual table based on record set of select statement. View cantain the field from on one or more than one table's fields. The using view we can use JOIN and where statement and IT' s looks like single table .
   Ex:- Create View view_name AS SELECT Column(s) from TABLEname where Condition
   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.
6. What is a "trigger"?
   
   Triggers are stored procedures that database should take action when relevant event occur
   In other word we can say trigger are stored procedure that fire when a relevant event occurs such as insertion , deletion, update
7. What is a "transaction"? Why are they necessary?
   
   Transactions are an atomic piece of instructions in SQL which have to be executed all or none.The word atomic signifies the all or none character of a transaction.
8. How to remove duplicate records from a table?
   
   delete from emp where en not in (select min(en) from emp order by columnname)
9. How will you copy the structure of a table without copying the data?
   
   select * Into NEWTABLE from OLDTABLE where 1=2
10. 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.
11. 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.
12. 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.
13. 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.

14. What are 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.
15. 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
16. 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.
17. 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.
18. 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.
19. 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.
20. What command do we use to rename a db? - sp_renamedb ‘oldname’ , ‘newname’
21. What is a Join in SQL Server? - Join actually puts data from two or more tables into a single result set.
22. Can you explain the types of Joins that we can have with Sql Server? - There are three types of joins: Inner Join, Outer Join, Cross Join
23. What is a Linked Server? - Linked Servers is a concept in SQL Server by which we can add other SQL Server to a Group and query both the SQL Server dbs using T-SQL Statements.
24. What are the OS services that the SQL Server installation adds? - MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac co-ordinator).