DELETE

DELETE

Deletes rows from a table.

Synopsis

DELETE FROM [ONLY] table [[AS] alias]
      [USING usinglist]
      [WHERE condition | WHERE CURRENT OF cursor_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.

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.

If the WHERE CURRENT OF clause is specified, the row that is deleted is the one most recently fetched from the specified cursor.

You must have the DELETE privilege on the table to delete from it.

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).

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 provided, 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 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 returning a value of type boolean, which determines the rows that are to 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 target table.
WHERE CURRENT OF cannot be specified together with a Boolean condition.
The DELETE...WHERE CURRENT OF cursor statement can only be executed on the server, for example in an interactive psql session or a script. Language extensions such as PL/pgSQL do not have support for updatable cursors.
See DECLARE for more information about creating cursors.

Notes

Greenplum Database lets you reference columns of other tables in the WHERE condition by specifying the other tables in the USING clause. For example, to the name Hannah from the rank table, one might do:

DELETE FROM rank USING names WHERE names.id = rank.id AND 
name = 'Hannah';

What is essentially happening here is a join between rank and names, with all successfully joined rows being marked for deletion. This syntax is not standard. However, this join style is usually easier to write and faster to execute than a more standard sub-select style, such as:

DELETE FROM rank WHERE id IN (SELECT id FROM names WHERE name 
= 'Hannah');

When using DELETE to remove all the rows of a table (for example: DELETE * FROM table;), Greenplum Database adds an implicit TRUNCATE command (when user permissions allow). The added TRUNCATE command frees the disk space occupied by the deleted rows without requiring a VACUUM of the table. This improves scan performance of subsequent queries, and benefits ELT workloads that frequently insert and delete from temporary tables.

Execution of UPDATE and DELETE commands directly on a specific partition (child table) of a partitioned table is not supported. Instead, these commands must be executed on the root partitioned table, the table created with the CREATE TABLE command.

Examples

Delete all films but musicals:

DELETE FROM films WHERE kind <> 'Musical';

Clear the table films:

DELETE FROM films;

Delete using a join:

DELETE FROM rank USING names WHERE names.id = rank.id AND 
name = 'Hannah';

Compatibility

This command conforms to the SQL standard, except that the USING clause is a Greenplum Database extension.

See Also

DECLARE, TRUNCATE