When to Use Truncate vs Delete: A Comprehensive Guide

The DELETE statement deletes rows one at a time and records an entry in the transaction log for each deleted row.

Truncate

TABLE removes the data by de-allocating the data pages used to store the table data and records only page deallocations in the transaction log. Everyone should be aware that DELETE is a DML command and TRUNCATE is a DDL command. DELETE deletes records one by one and makes an entry for each and every deletion in the transaction log, while TRUNCATE deallocates pages and creates an entry for page deallocation in the transaction log.

When it comes to SQL Server, there are two ways to delete rows from a table: using the TRUNCATE and DELETE commands. Although both commands have the same end result, there are some important differences that you should be aware of. Delete is a DML command, while truncate is a DDL command. Truncate can be used to delete all data from the table without maintaining the integrity of the table.

On the other hand, the delete statement can be used to delete specific data. With the delete command we cannot bypass integrity enforcement mechanisms. The truncate statement is a data definition language or DDL command that is used to delete entire data from the table without deleting the table structure. TRUNCATE TABLE locks the entire table to delete data from a table; therefore, this command also uses less transaction space than DELETE.

Therefore, truncation cannot be undone, and an error in the truncation process will have issued a confirmation anyway. The DELETE statement can have a WHERE clause to delete specific records, while the TRUNCATE statement does not require any and deletes the entire table. Rows deleted by the TRUNCATE TABLE statement cannot be restored, and you cannot specify the where clause in the TRUNCATE statement. TRUNCATE transactions can be reversed in database engines such as SQL Server and PostgreSQL, but not in MySQL and Oracle. A TRUNCATE should never be used if a delete trigger is defined in the table to perform any automatic cleanup or logging action when rows are deleted. So when it comes to deciding between using Delete or Truncate, it's important to understand their differences.

Delete does not affect the identifier of the data object, but truncate assigns a new data object identifier unless there has never been an insertion into the table since its creation. Even a single insertion that is reverted will cause a new data object identifier to be assigned when truncated. I recommend using a DELETE statement in all cases, except in those special circumstances that deserve a TRUNCATE. If I remember correctly, the TRUNCATE statement will delete all rows AND the space used by the rows (in other words, it will deallocate space).The main difference between them is that the delete statement deletes data without restoring the identity of a table, while the truncate command restores the identity of a particular table.

However, I have seen unintentionally truncating referential integrity and violating other constraints. In conclusion, it's important to understand when it's appropriate to use either Delete or Truncate when deleting rows from a table in SQL Server. Delete is best used when you need to delete specific records from a table, while Truncate should be used when you need to delete all records from a table without maintaining its integrity.