MySQL：子查詢返回多個行

Question

我需要在更新問題表後刪除響應表中的行，但出現此錯誤：子查詢返回多個行。有沒有辦法讓它工作？

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

更改=到= 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 2

使用 「在」：

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); 

或限制你的子查詢，以便它只返回一行。

Answer 3

是，使用JOIN代替：

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 4

您可以通過限制或不同的子查詢的結果限制爲1，或者如果你ened刪除子查詢所有創立的結果，你需要使用WHERE id IN (....)