Delete table is a registered operation, meaning that the deletion of each row is recorded in the transaction log, making it slower than truncate table. Truncate also deletes all rows from a table, but it does not record the deletion of each row, instead recording the deallocation of the table's data pages, making it faster. The Delete command is slower than the Truncate command. It's faster than the delete command because when interviewing SQL Server candidates, most don't know some of the basic differences between SQL Server's delete and truncate commands, as well as whether these operations can be undone.
Delete is a DML command, whereas truncate is a DDL command. Truncate can be used to remove all data from the table without maintaining the integrity of the table. Alternatively, the delete statement can be used to delete specific data. With the delete command, we can't bypass integrity compliance mechanisms.
The DELETE statement analyzes each row before deleting it, making it slower compared to the TRUNCATE command. If we want to delete all the records in a table, it is preferable to use TRUNCATE instead of DELETE, since the first one is faster than the second. Truncate will remove the watermark along with the records from the database, however, the Delete statement will delete only the records. The reversal cannot be done when truncating because it is an implicit confirmation where the reversal occurs when deleting.
The Truncate command resets the highest watermark in the segment and releases the space, while deleting does not restore the highest watermark. It means that when you use the Delete statement, only the records are deleted, but the memory used by those records in the table will not be modified. DELETE deletes records one by one and creates an entry for each and every deletion in the transaction log, while TRUNCATE demaps pages and creates an entry for de-mapping pages in the transaction log. TRUNCATE is faster than DELETE because truncate does not record the rows that are deleted, whereas DELETE keeps a record of the deleted rows until the transaction is committed.
The DROP statement is a data definition language (DDL) command used to delete existing database objects. Truncating is faster than deleting because it does not require a WHERE clause like delete does; delete requires looking through an entire table for a particular WHERE clause and deleting that particular record or records. In conclusion, when deleting all records from a table, it is preferable to use TRUNCATE instead of DELETE due to its speed and efficiency. However, if you need to delete specific records from a table then DELETE should be used instead.
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