Question

我需要在更新问题表后从响应表中删除行但是我收到此错误：子查询返回多行。有没有办法让它发挥作用？

CREATE TRIGGER delete_responses AFTER UPDATE ON  questions
FOR EACH ROW 
BEGIN 
IF NEW.active != OLD.active 
THEN DELETE FROM responses WHERE option_id = (
SELECT option_id
FROM options
WHERE question_id = OLD.question_id);

Answer 1

是的，请改用JOIN：

DELETE r
FROM responses AS r
INNER JOIN options AS o ON r.option_id = o.option_id
WHERE o.question_id = OLD.question_id;

Answer 2

将=更改为= ANY或in：

CREATE TRIGGER delete_responses AFTER UPDATE ON  questions
FOR EACH ROW 
BEGIN 
IF NEW.active != OLD.active 
THEN DELETE FROM responses WHERE option_id in (
SELECT option_id
FROM options
WHERE question_id = OLD.question_id);

Answer 3

使用“in”：

CREATE TRIGGER delete_responses AFTER UPDATE ON  questions
FOR EACH ROW 
BEGIN 
IF NEW.active != OLD.active 
THEN DELETE FROM responses WHERE option_id in (
SELECT option_id
FROM options
WHERE question_id = OLD.question_id);

或限制子查询，使其只返回一行。

Answer 4

您可以通过限制或不同将子查询的结果限制为1，或者如果您要删除子查询中的所有已创建结果，则需要使用WHERE id IN (....)

MySQL：子查询返回多行

4 个答案: