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Difference between DELETE and TRUNCATE commands

Posted by Vithal Wadje Blogs | SQL Nov 23, 2012
In this blog I have explained the difference between DELETE and TRUNCATE commands in SQL Server.

Background

Many times in interview ,interviewer asked the question difference between DELETE and TRUNCATE commands,at that time freshers or any expericed candidate may be confuse how to give answer by differntciating between two commands ,so by considering above requirement i have decided to write this blog to help job seeker and who wants to know what is the diiffrence between the two commands, so let us see.

Truncate command

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.

Following are the some keypoints

  1. TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.
  2. 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.
  3. TRUNCATE removes all rows from a table, but the table structure, its columns, constraints, indexes and so on, remains. The counter used by an identity for new rows is reset to the seed for the column.
  4. 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.
  5. TRUNCATE cannot be rolled back.
  6. TRUNCATE is DDL Command.
  7. TRUNCATE Resets identity of the table

Delete command

Delete command removes the rows from a table based on the condition that we provide with a WHERE clause.

Following are the some keypoints

  1. DELETE removes rows one at a time and records an entry in the transaction log for each deleted row.
  2. 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.
  3. DELETE Can be used with or without a WHERE clause
  4. DELETE Activates Triggers.
  5. DELETE can be rolled back.
  6. DELETE is DML Command.
  7. DELETE does not reset identity of the table.
Note: DELETE and TRUNCATE both can be rolled back when surrounded by TRANSACTION if the current session is not closed. If TRUNCATE is written in Query Editor surrounded by TRANSACTION and if session is closed, it can not be rolled back but DELETE can be rolled back.

Summary

I hope this small blog is helpful for all jobseeker and othe reader, if you have any suggestion then please contact me.

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