Why Truncate is faster than Delete?

Delete & Truncate

DELETE is a logged operation on a per row basis. This means that the deletion of each row gets logged and physically deleted.

You can DELETE any row that will not violate a constraint, while leaving the foreign key or any other constraint in place.

TRUNCATE is also a logged operation, but in a different way. TRUNCATE logs the deallocation of the data pages in which the data exists. The deallocation of data pages means that your data rows still actually exist in the data pages, but the extents have been marked as empty for reuse. This is what makes TRUNCATE a faster operation to perform over DELETE.

You cannot TRUNCATE a table that has any foreign key constraints. You will have to remove the constraints, TRUNCATE the table, and reapply the constraints.

TRUNCATE will reset any identity columns to the default seed value. This means if you have a table with an identity column and you have 264 rows with a seed value of 1, your last record will have the value 264 (assuming you started with value 1) in its identity columns. After TRUNCATEing your table, when you insert a new record into the empty table, the identity column will have a value of 1. DELETE will not do this. In the same scenario, if your rows are deleted, when inserting a new row into the empty table, the identity column will have a value of 265.

Why Truncate is faster than Delete?

Reason:When you type DELETE all the data get copied into the Rollback Table space first, then delete operation is performed. So when you type ROLLBACK after deleting a table ,you can get back the data(The system get it for you from the Rollback Tables pace).All this process take time, but when we use TRUNCATE, it removes data directly without copying it into the Rollback Table space. So TRUNCATE is faster. Once you Truncate you can't get back the data.