Postgres:仅检查 INSERT 的约束 [英] Postgres: Constraint with check on INSERT only

问题描述

我需要在 Postgres 中设置一个约束，它只会在 INSERT 查询上触发(而不是在 UPDATE 查询上).

I need a constraint in Postgres which would be triggered on INSERT queriesonly (not on UPDATE queries).

目前它是这样实现的:

ALTER TABLE test ADD CONSTRAINT check_something_const 
CHECK (check_something(id, task_id)) NOT VALID;

哪里check_something

CREATE OR REPLACE FUNCTION check_something(UUID, UUID)
RETURNS BOOLEAN AS $$
DECLARE
existed_id UUID;
BEGIN
SELECT id
INTO existed_id
FROM test WHERE ...etc. 
RETURN existed_id IS NULL
END;
$$ LANGUAGE 'plpgsql' VOLATILE;

目前 check_something_const 在更新和插入查询时都会被触发.我需要的是在插入新行但不更新时仅检查此项.

And currently check_something_const is triggered both on update and insert queries. What I need is this to be checked only when new rows are inserted, but not updated.

推荐答案

这可以通过仅在插入时触发的触发器过程来实现.

This can be achieved with a trigger procedure that fires on insert only.

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