CREATE RULE
Function
CREATE RULE defines a new rewriting rule.
Precautions
- To define or modify rules for a table, you must be the owner of the table.
- If multiple rules of the same type are defined for the same table, the rules are triggered one by one by name in alphabetical order.
- In the view, the RETURNING clause can be added to the INSERT, UPDATE, and DELETE rules to return columns by view. If a rule is triggered by the INSERT RETURNING, UPDATE RETURNING, or DELETE RETURNING command, these clauses are used to calculate the output result. If a rule is triggered by a command without RETURNING, the RETURNING clause of the rule is ignored. Currently, only unconditional INSTEAD rules can contain the RETURNING clause, and only one RETURNING clause can exist in all rules of one event. This ensures that only one RETURNING clause can be used for result calculation. If the RETURNING clause does not exist in any valid rule, the RETURNING query in this view will be rejected.
Syntax
CREATE [ OR REPLACE ] RULE name AS ON event
TO table_name [ WHERE condition ]
DO [ ALSO | INSTEAD ] { NOTHING | command | ( command ; command ... ) }
Events include:
SELECT
INSERT
DELETE
UPDATE
Parameter Description
name
Name of the created rule. It must be unique among all the rules for the same table.
Value range: a string, which complies with the identifier naming convention. A value can contain a maximum of 63 characters.
table_name
Name (optionally schema-qualified) of the table or view to which the rule applies.
condition
SQL condition expression that returns a Boolean value, which determines whether to execute the rule. Expressions cannot reference any table except NEW and OLD, and cannot have aggregate functions.
INSTEAD
INSTEAD indicates that the initial event is replaced with this command.
ALSO
ALSO indicates that the command should be executed after the initial event. If neither ALSO nor INSTEAD is specified, ALSO is the default value.
command
Command that composes the rule action. A valid command is one of the SELECT, INSERT, UPDATE, and DELETE statements.
Examples
CREATE RULE "_RETURN" AS
ON SELECT TO t1
DO INSTEAD
SELECT * FROM t2;