DELETE() SQL Commands DELETE()
NAME
DELETE - delete rows of a table
SYNOPSIS
DELETE FROM [ ONLY ] table [ [ AS ] alias ]
[ USING usinglist ]
[ WHERE condition | WHERE CURRENT OF cursor_name ]
[ RETURNING * | output_expression [ AS output_name ] [, ...] ]
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.
Tip: TRUNCATE [truncate(l)] is a PostgreSQL extension that pro-
vides a faster mechanism to remove all rows from a 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 men-
tioned, you must use the ONLY clause.
There are two ways to delete rows in a table using information con-
tained in other tables in the database: using sub-selects, or specify-
ing 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.
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.
PARAMETERS
ONLY If specified, delete rows from the named table only. When not
specified, any tables inheriting from the named table are also
processed.
table The name (optionally schema-qualified) of an existing table.
alias A substitute name for the target table. When an alias is pro-
vided, it completely hides the actual name of the table. For
example, given DELETE FROM foo AS f, the remainder of the DELETE
statement must refer to this table as f not foo.
usinglist
A list of table expressions, allowing columns from other tables
to appear in the WHERE condition. This is similar to the list of
tables that can be specified in the FROM Clause [select(l)] of a
SELECT statement; for example, an alias for the table name can
be specified. Do not repeat the target table in the usinglist,
unless you wish to set up a self-join.
condition
An expression that returns a value of type boolean. Only rows
for which this expression returns true will be deleted.
cursor_name
The name of the cursor to use in a WHERE CURRENT OF condition.
The row to be deleted is the one most recently fetched from this
cursor. The cursor must be a simple (non-join, non-aggregate)
query on the DELETE's target table. Note that WHERE CURRENT OF
cannot be specified together with a Boolean condition.
output_expression
An expression to be computed and returned by the DELETE command
after each row is deleted. The expression can use any column
names of the table or table(s) listed in USING. Write * to
return all columns.
output_name
A name to use for a returned column.
OUTPUTS
On successful completion, a DELETE command returns a command tag of the
form
DELETE count
The count is the number of rows deleted. If count is 0, no rows matched
the condition (this is not considered an error).
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.
NOTES
PostgreSQL lets you reference columns of other tables in the WHERE con-
dition 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 produc-
ers, 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.
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 posi-
tioned:
DELETE FROM tasks WHERE CURRENT OF c_tasks;
COMPATIBILITY
This command conforms to the SQL standard, except that the USING and
RETURNING clauses are PostgreSQL extensions.
SQL - Language Statements 2008-09-19 DELETE()
postgresql 8.3.4 - Generated Fri Oct 3 18:56:37 CDT 2008