我的扳机有问题。插入新行时,它将检查商品是否尚未售出。我可以在软件中做到这一点,但我认为当数据库做到这一点时效果会更好。
-- Create function
CREATE OR REPLACE FUNCTION checkSold() RETURNS TRIGGER AS $checkSold$
BEGIN
SELECT offer_id FROM offer WHERE offer_id = NEW.offer_id AND date_sale IS NULL;
IF NOT FOUND THEN
RAISE EXCEPTION 'The Offer is Sold!';
END IF;
RETURN NEW;
END;
$checkSold$ LANGUAGE plpgsql;
-- Create trigger
Drop TRIGGER checkSold ON tag_map;
CREATE TRIGGER checkSold BEFORE INSERT ON tag_map FOR EACH ROW EXECUTE PROCEDURE checkSold();
INSERT INTO tag_map (tag_id,offer_id) VALUES (824,80);
这是插入后的错误。
[WARNING ] INSERT INTO tag_map (tag_id,offer_id) VALUES (824,80)
ERROR: query has no destination for result data
HINT: If you want to discard the results of a SELECT, use PERFORM instead.
CONTEXT: PL/pgSQL function "checksold" line 2 at SQL statement
触发器有什么问题?没有它,效果很好。
最佳答案
代替
SELECT offer_id FROM offer WHERE offer_id = NEW.offer_id AND date_sale IS NULL;
和
PERFORM offer_id FROM offer WHERE offer_id = NEW.offer_id AND date_sale IS NULL;
按照建议。
手册中的更多信息("38.5.2. Executing a Command With No Result")。