Other Definition Sql Server

What is the difference between clustered and a non-clustered index?

A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.

A nonclustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a nonclustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.

What is cursors?

Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time.
In order to work with a cursor we need to perform some steps in the following order:

1. Declare cursor
2. Open cursor
3. Fetch row from the cursor
4. Process fetched row
5. Close cursor
6. Deallocate cursor

What’s the difference between a primary key and a unique key?

Both primary key and unique enforce uniqueness of the column on which they are defined.
But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default.
Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only.

What is 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.

TRUNCATETRUNCATE is faster and uses fewer system and transaction log resources than DELETE.
TRUNCATE removes the data by deallocating the data pages used to store the table’s data, and only the page deallocations are recorded in the transaction log.
TRUNCATE removes all rows from a table, but the table structure and its columns, constraints, indexes and so on remain.
The counter used by an identity for new rows is reset to the seed for the column.
You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint.
Because TRUNCATE TABLE is not logged, it cannot activate a trigger.TRUNCATE can not be Rolled back using logs.
TRUNCATE is DDL Command.TRUNCATE Resets identity of the table.
DELETEDELETE removes rows one at a time and records an entry in the transaction log for each deleted row.
If you want to retain the identity counter, use DELETE instead.
If you want to remove table definition and its data, use the DROP TABLE statement.DELETE Can be used with or without a WHERE clauseDELETE Activates Triggers.
DELETE Can be Rolled back using logs.DELETE is DML Command.
DELETE does not reset identity of the table.

Difference between Function and Stored Procedure?

UDF can be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section where as Stored procedures cannot be.
UDFs that return tables can be treated as another rowset.
This can be used in JOINs with other tables.Inline UDF’s can be though of as views that take parameters and can be used in JOINs and other Rowset operations.