DELETE FROM [ ONLY ] table [ USING usinglist ] [ WHERE condition ]
DELETE deletes rows that satisfy the WHERE clause from the specified table. If the WHERE clause is absent, the effect is to delete all rows in the table. The result is a valid, but empty table.
By default, DELETE will delete rows in the specified table and all its child tables. If you wish to delete only from the specific table mentioned, you must use the ONLY clause.
There are two ways to delete rows in a table using information contained in other tables in the database: using sub-selects, or specifying additional tables in the USING clause. Which technique is more appropriate depends on the specific circumstances.
You must have the DELETE privilege on the table to delete from it, as well as the SELECT privilege for any table in the USING clause or whose values are read in the condition.
On successful completion, a DELETE command returns a command tag of the form
DELETE countThe count is the number of rows deleted. If count is 0, no rows matched the condition (this is not considered an error).
PostgreSQL lets you reference columns of other tables in the WHERE condition by specifying the other tables in the USING clause. For example, to delete all films produced by a given producer, one might do
DELETE FROM films USING producers WHERE producer_id = producers.id AND producers.name = 'foo';What is essentially happening here is a join between films and producers, with all successfully joined films rows being marked for deletion. This syntax is not standard. A more standard way to do it is
DELETE FROM films WHERE producer_id IN (SELECT id FROM producers WHERE name = 'foo');In some cases the join style is easier to write or faster to execute than the sub-select style.
Delete all films but musicals:
DELETE FROM films WHERE kind <> 'Musical';
Clear the table films:
DELETE FROM films;
This command conforms to the SQL standard, except that the USING clause and the ability to reference other tables in the WHERE clause are PostgreSQL extensions.