DELETE
Deletes rows from a table.
Synopsis
[WITH [RECURSIVE] <with_query> [, ...]]
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.
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.
The WHERE CURRENT OF clause is not supported with replicated tables.
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.
The RETURNING clause is not supported when deleting from append-optimized tables.
You must have the DELETE privilege on the table to delete from it.
As the default, Greengage DB acquires an EXCLUSIVE lock on tables for DELETE operations on heap tables.
When the Global Deadlock Detector is enabled, the lock mode for DELETE operations on heap tables is ROW EXCLUSIVE.
Outputs
On successful completion, a DELETE command returns a command tag of the form:
DELETE <count>
where count is the number of rows deleted.
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.
Parameters
| Parameter | Description |
|---|---|
with_query |
The For a See Common table expressions and SELECT for details |
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 |
usinglist |
A list of table expressions, allowing columns from other tables to appear in the |
condition |
An expression returning a value of type |
cursor_name |
The name of the cursor to use in a
The See DECLARE for more information about creating cursors |
output_expression |
An expression to be computed and returned by the |
output_name |
A name to use for a returned column |
Notes
Greengage DB lets you reference columns of other tables in the WHERE condition by specifying the other tables in the USING clause.
For example, to delete the row with the name Hannah from the rank table, run:
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 run than a more standard sub-select style, such as:
DELETE FROM rank
WHERE id IN (SELECT id FROM names WHERE name = 'Hannah');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 run on the root partitioned table, the table created with the CREATE TABLE command.
For a partitioned table, all the child tables are locked during the DELETE operation when the Global Deadlock Detector is not enabled (the default).
Only some of the leaf child tables are locked when the Global Deadlock Detector is enabled.
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 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 and RETURNING clauses are Greengage DB extensions, as is the ability to use WITH with DELETE.