DELETE is a DML command that removes rows individually, supports WHERE clauses, logs each deletion, allows rollback, and fires triggers; 2. TRUNCATE is a DDL-like command that deallocates pages, removes all data without conditions, minimally logs operations, resets identity seeds, doesn’t fire triggers, and requires higher privileges; 3. TRUNCATE is faster for full-table deletes but lacks conditional filtering and referential integrity flexibility, making DELETE better for selective removals and TRUNCATE ideal for quick, complete table clearance.
DELETE and TRUNCATE are both used to remove data from a table in SQL, but they work differently and have important distinctions in behavior, performance, and usage.
How DELETE Works
DELETE is a DML (Data Manipulation Language) command that removes rows one at a time based on a condition. If no WHERE clause is specified, it deletes all rows but still processes them individually.
- You can use a WHERE clause to filter which rows to delete.
- Each deleted row is logged in the transaction log, allowing rollback.
- Triggers can be fired during a DELETE operation.
- It retains the table structure and resets identity seeds only if explicitly reset.
- Slower than TRUNCATE for large datasets due to row-by-row processing.
How TRUNCATE Works
TRUNCATE is a DCL (Data Control Language) command that removes all rows from a table by deallocating data pages, not individual rows.
- It always removes all data—no WHERE clause allowed.
- Minimal logging: only page deallocations are recorded, making it faster.
- Resets identity counters to initial seed value.
- Cannot fire triggers since it doesn’t process rows individually.
- Requires higher permissions (e.g., ALTER) and cannot be used on tables with foreign key references.
Key Differences Summary
Understanding when to use each matters for performance and integrity.
- Logging: DELETE logs row deletions; TRUNCATE logs page deallocations.
- Speed: TRUNCATE is faster for clearing entire tables.
- Rollback: Both can be rolled back if in a transaction.
- Conditions: DELETE supports WHERE; TRUNCATE does not.
- Triggers: DELETE respects triggers; TRUNCATE does not activate them.
- Identity Columns: TRUNCATE resets identity values; DELETE does not.
Choose DELETE when you need conditional removal or trigger support. Use TRUNCATE when quickly emptying a whole table and resetting auto-increment values. The choice affects performance, logging, and referential integrity.
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