What is the Difference Between Delete and Truncate?

Learn about what is difference between delete and truncate commands and how they are used for deleting data from tables.

What is the Difference Between Delete and Truncate?

The DELETE statement deletes the rows one at a time and records one entry in the transaction log for each deleted row. On the other hand, TRUNCATE TABLE removes the data by demapping the data pages used to store the table data and records only page deallocations in the transaction log. The DELETE command is slower than the TRUNC command. Truncate unmaps all pages of data in a table.

Therefore, it removes all statistics and also the allocated space. Both Delete and Truncate commands can be used to delete data from the table. 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. Therefore, it is 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. By issuing a TRUNCATE TABLE statement, you instruct SQL Server to delete all records in a table, without any logging or transaction processing taking place. Note that we can't use the truncate statement when a foreign key references a table or participates in an indexed view. I need to test your statement that TRUNCATE resets IDENTITY seeds, I also need to test if TRUNCATE will follow cascading deletions for the foreign key RI.

There are many ways to delete data in SQL, including the DELETE, TRUNCATE TABLE, and DROP TABLE commands. When partitioning a table, individual partitions can be truncated in isolation, making it possible to partially delete all of the data in the table. In PostgreSQL, you need the TRUNC privilege; in SQL Server, the minimum permission is ALTER table; in MySQL, you need the DROP privilege. If you have a foreign key constraint that references the table you are trying to truncate, it will not work even if the reference table contains no data.

The problem is that not many know it, so they will most likely consider the answer to be incorrect if you tell them that YES Truncating can be undone. TRUNCATE cannot be used in the table referenced by a FOREIGN KEY constraint, unless a table has a foreign key that references itself. Truncating table also deletes all the rows in a table, but it will not record the deletion of each row, but it will record the deallocation of the table's data pages, making it faster.

Charlotte Wilson
Charlotte Wilson

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