DROP TABLE vs TRUNCATE TABLE

Both remove data, but they do very different things.

DROP TABLE — Delete the Table Entirely

Removes the table's structure and all its data — the table stops existing.

DROP TABLE employees;
DROP TABLE IF EXISTS employees;  -- no error if it's already gone

If another table has a foreign key pointing at this one, DROP TABLE fails unless you cascade the drop:

DROP TABLE customers CASCADE;
-- also drops any foreign key constraints (and dependent views) referencing customers

TRUNCATE TABLE — Empty the Table, Keep the Structure

Removes every row but leaves the table itself (columns, constraints, indexes) intact — ready to be filled with new data immediately.

TRUNCATE TABLE employees;

• It's far faster than DELETE FROM employees; for large tables, since it doesn't scan or log row-by-row.
• It also resets any SERIAL/identity sequence back to its starting value:

TRUNCATE TABLE employees RESTART IDENTITY;

• Truncating a table referenced by a foreign key needs CASCADE too, unless the referencing table is empty:

TRUNCATE TABLE customers CASCADE;

Quick Comparison

	DROP TABLE	TRUNCATE TABLE	DELETE FROM
Removes data	Yes	Yes	Yes (optionally filtered)
Removes table structure	Yes	No	No
Speed on large tables	N/A	Very fast	Slower
Resets auto-increment IDs	N/A	With RESTART IDENTITY	No
Can filter with WHERE	No	No	Yes

Common Errors & Troubleshooting

• ERROR: cannot truncate a table referenced in a foreign key constraint — add CASCADE to also truncate the referencing tables, or truncate the child tables first, in dependency order.
• Realizing too late that TRUNCATE isn't transactional the way you expected — it IS transactional (rollback-able inside BEGIN/COMMIT) in PostgreSQL, unlike some other databases — but it still can't be filtered with a WHERE clause, so don't reach for it when you only meant to delete some rows.
• DROP TABLE failing with "cannot drop table because other objects depend on it" — a view or foreign key elsewhere depends on this table; either drop those first, or add CASCADE if removing them too is intended.

Key Takeaways

• DROP TABLE removes the table itself; TRUNCATE empties it but keeps its structure.
• TRUNCATE is dramatically faster than DELETE FROM table with no WHERE clause, on large tables.
• Both may need CASCADE if other tables have foreign keys pointing at the one you're removing.