mysql - MySQL：子查询返回多于一行

Question

更新问题表后，我需要从响应表中删除行，但出现此错误：子查询返回多行。有没有办法让它工作？

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JOIN改用：

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

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

用于”：

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);

或限制您的子查询，使其仅返回一行。

Answer 4

您可以通过 limit 或 distinct 将子查询的结果限制为 1，或者如果您想删除需要使用的子查询中的所有已创建结果WHERE id IN (....)