DELETE
DELETE — delete rows of a table
Synopsis
[ WITH [ RECURSIVE ] with_query [, ...] ]
DELETE FROM [ ONLY ] table_name [ * ] [ [ AS ] alias ]
[ USING from_item [, ...] ]
[ 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.
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
with_query
The
WITH
clause allows you to specify one or more subqueries that can be referenced by name in theDELETE
query. See Section 6.8") and SELECT for details.table_name
The name (optionally schema-qualified) of the table to delete rows from. If
ONLY
is specified before the table name, matching rows are deleted from the named table only. IfONLY
is not specified, matching rows are also deleted from any tables inheriting from the named table. Optionally,*
can be specified after the table name to explicitly indicate that descendant tables are included.alias
A substitute name for the target table. When an alias is provided, it completely hides the actual name of the table. For example, given
DELETE FROM foo AS f
, the remainder of theDELETE
statement must refer to this table asf
notfoo
.from_item
A table expression allowing columns from other tables to appear in the
WHERE
condition. This uses the same syntax as the FROM clause of aSELECT
statement; for example, an alias for the table name can be specified. Do not repeat the target table as afrom_item
unless you wish to set up a self-join (in which case it must appear with an alias in thefrom_item
).condition
An expression that returns a value of type
boolean
. Only rows for which this expression returnstrue
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 non-grouping query on theDELETE
's target table. Note thatWHERE 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 named bytable_name
or table(s) listed inUSING
. 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. 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 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
ProtonBase 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.
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;
Compatibility
This command conforms to the SQL standard, except that the USING
and RETURNING
clauses are ProtonBase extensions, as is the ability to use WITH
with DELETE
.