Description

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.

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.

The optional RETURNING clause causes DELETE to compute and return value(s) based on each row actually deleted. Any expression using the table's columns, and/or columns of other tables mentioned in USING, can be computed. The syntax of the RETURNING list is identical to that of the output list of SELECT.

If the FOR PORTION OF clause is used, the delete will only affect rows that overlap the given portion. Furthermore, if a row's application time extends outside the FOR PORTION OF bounds, then the delete will only change the application time within those bounds. In effect, only the history targeted by FOR PORTION OF is deleted, and no moments outside. Furthermore, after a row is deleted, new temporal leftovers might be inserted: rows whose range or multirange receives the remaining application time outside the targeted bounds, with the original values in their other columns. For range columns, there will be zero to two inserted records, depending on whether the original application time was completely deleted, extended before/after the change, or both. Multiranges never require two temporal leftovers, because one value can always contain whatever application time remains.

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. When FOR PORTION OF is used, the secondary inserts do not require INSERT privilege on the table. (This is because conceptually no new information is being added; the inserted rows only preserve existing data about the untargeted time period.)

Parameters

Outputs

On successful completion, a DELETE command returns a command tag of the form

DELETE count

The count is the number of rows deleted. Note that the number may be less than the number of rows that matched the condition when deletes were suppressed by a BEFORE DELETE trigger. If count is 0, no rows were deleted by the query (this is not considered an error). If FOR PORTION OF was used, the count does not include temporal leftovers that were inserted.

If the DELETE command contains a RETURNING clause, the result will be similar to that of a SELECT statement containing the columns and values defined in the RETURNING list, computed over the row(s) deleted by the command. If FOR PORTION OF was used, the RETURNING clause gives one result for each deleted row, but does not include inserted temporal leftovers. The value of the application-time column matches the old value of the deleted row(s). Note this will represent more application time than was actually erased, if temporal leftovers were inserted.

Notes

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 can 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.

When FOR PORTION OF is used, this can result in users who don't have INSERT privileges firing INSERT triggers. This should be considered when using SECURITY DEFINER trigger functions.

Examples

Delete all films but musicals:

DELETE FROM films WHERE kind <> 'Musical';

Clear the table films:

DELETE FROM films;

Delete completed tasks, returning full details of the deleted rows:

DELETE FROM tasks WHERE status = 'DONE' RETURNING *;

Delete the row of tasks on which the cursor c_tasks is currently positioned:

DELETE FROM tasks WHERE CURRENT OF c_tasks;

An example of a temporal delete:

DELETE FROM products
  FOR PORTION OF valid_at FROM '2021-08-01' TO '2023-09-01'
  WHERE product_no = 5;

While there is no LIMIT clause for DELETE, it is possible to get a similar effect using the same method described in the documentation of UPDATE:

WITH delete_batch AS (
  SELECT l.ctid FROM user_logs AS l
    WHERE l.status = 'archived'
    ORDER BY l.creation_date
    FOR UPDATE
    LIMIT 10000
)
DELETE FROM user_logs AS dl
  USING delete_batch AS del
  WHERE dl.ctid = del.ctid;

This use of ctid is only safe because the query is repeatedly run, avoiding the problem of changed ctids.

Compatibility

This command conforms to the SQL standard, except that the USING and RETURNING clauses are PostgreSQL extensions, as is the ability to use WITH with DELETE.

See Also