Wednesday, June 23, 2004

Delete Vs Truncate Statement

• Delete table is a logged operation, so the deletion of each row gets logged in the transaction log, which makes it slow.

• Truncate table also deletes all the rows in a table, but it won’t log the deletion of each row, instead it logs the de-allocation of the data pages of the table, which makes it faster. Truncate table can be rolled back if it happens within a Transaction.

• Truncate table is functionally identical to delete statement with no “where clause” both remove all rows in the table. But truncate table is faster and uses fewer system and transaction log resources than delete.

• Truncate table removes all rows from a table, but the table structure and its columns, constraints, indexes etc., remains as it is.

• In truncate table the counter used by an identity column for new rows is reset to the seed for the column.

• If you want to retain the identity counter, use delete statement instead.

• If you want to remove table definition and its data, use the drop table statement.

• You cannot use truncate table on a table referenced by a foreign key constraint; instead, use delete statement without a where clause. Because truncate table is not logged, it cannot activate a trigger.

• Truncate table may not be used on tables participating in an indexed view.

9 comments:

Anonymous said...

This is a nice technical article.

Thanks!!
Vignesh

Ankit Dangi said...

Thanks, a good one.

Vinny said...

nice.ty

anuradhu said...

very gud one!quite informative!

anuradhu said...

very informative!Thanks!

Anonymous said...

Nice list, however it is misleading in that TRUNCATE TABLE can be rolled back within a transaction. TRUNCATE TABLE however cannot be rolled back after a transaction is committed by using the transaction log.

Vadivel said...

Hello Anonymous :) Truncate information can also be rolledback if it happens within a transaction.

Check out my other blog post on this topic here - http://vadivel.blogspot.com/2006/12/rolling-back-truncate-operation.html

Chidamparam said...

My requirement is: create a temp table, insert data, take a dump, move it to another DB, then truncate the table and then Insert the data and then the above cycle continues periodically.
Finding performance issue due to long duration of truncate.

Can I use drop table instead of truncate ?
any other alternate approach to meet the above requirement

sourabh deepraj said...

Hi Vadivel,
i have heard that delete can be rolled back.
If i want to roll back delete statement,How can i do that without keeping in transaction block?

that is without using--

begin transaction
delete from table1
rollback transaction