The DELETE and TRUNCATE commands are both used to remove data from tables in SQL, but they work differently and have distinct characteristics. Here are the main differences between the two:
1. Syntax
- DELETE: The syntax usually includes a WHERE clause to specify which rows to delete.
DELETE FROM table_name WHERE condition;
- TRUNCATE: The syntax does not allow for a WHERE clause and removes all rows from a table.
TRUNCATE TABLE table_name;
2. Operation
- DELETE: This command removes rows one at a time and can be rolled back if used within a transaction. It logs each row deletion, which can be slower for large datasets.
- TRUNCATE: This command removes all rows from a table without logging individual row deletions. It is faster than DELETE as it typically deallocates the data pages instead of logging each row.
3. Transaction Logging
- DELETE: Fully logged; each deleted row is recorded in the transaction log. This means it can be rolled back if necessary.
- TRUNCATE: Minimally logged; it only logs the page deallocation, making it more efficient but less granular in terms of recovery options.
4. Performance
- DELETE: Generally slower for large tables, especially if there are a large number of rows to delete.
- TRUNCATE: Performs better since it doesn’t scan each row and delete them individually.
5. Referential Integrity
- DELETE: Can be used when there are foreign key constraints; if a row is deleted that is referenced by another table, you must ensure that referential integrity is maintained.
- TRUNCATE: Cannot be used when there are foreign key constraints referencing the table. You must drop or disable foreign keys before truncating.
6. Identity Reset
- DELETE: Does not reset any identity columns (if applicable).
- TRUNCATE: Resets identity columns to the seed value defined in the table.
Conclusion
In summary, use DELETE when you need to selectively remove rows and maintain transactional control, and use TRUNCATE when you want to quickly remove all rows from a table and do not need to preserve individual row deletion logs or maintain foreign key constraints.