Tuesday, March 25, 2008

Delete Vs Truncate Statement in Oracle

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. Of course, truncate table cannot be rolled back.

• 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.

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