Question

我正在尝试一个小时，但我仍然无法弄清楚此查询中的问题是什么。：/

SELECT * FROM question ORDER BY question_id DESC LIMIT 3 WHERE topic_name = (SELECT * FROM topic WHERE subject_name = 'Maths')

这是错误：

1064 - 您的SQL语法出错;检查与MySQL服务器版本对应的手册，以获得正确的语法 'WHERE topic_name =附近（SELECT * FROM主题WHERE subject_name = '数学'）'在第1行

Answer 1

你的陈述都是乱的。正确的陈述是：

SELECT *
FROM question
WHERE topic_name = (SELECT * FROM topic WHERE subject_name = 'Maths')
ORDER BY question_id DESC LIMIT 3 ;

但是，由于子查询，这不起作用。也许你的意思是：

SELECT *
FROM question
WHERE topic_name in (SELECT topic_name FROM topic WHERE subject_name = 'Maths')
ORDER BY question_id DESC LIMIT 3 ;

Answer 2

您的WHERE子句需要在ORDER BY子句之前：

SELECT * FROM question WHERE topic_name IN (SELECT topic_name FROM topic WHERE subject_name = 'Maths') ORDER BY question_id DESC LIMIT 3

Answer 3

指定哪个列并将结果限制为一个或使用IN运算符

SELECT * FROM question 
WHERE topic_name = (SELECT topic FROM topic WHERE subject_name = 'Maths')
ORDER BY question_id DESC LIMIT 1 

SELECT * FROM question 
WHERE topic_name in(SELECT topic FROM topic WHERE subject_name = 'Maths')
ORDER BY question_id DESC LIMIT 3

实际上这不是最佳建议。改为进行内连接：

SELECT * FROM question q
INNER JOIN topic t 
ON q.topic_name = t.topic
WHERE subject_name = 'Maths'
ORDER BY question_id LIMIT 3

无法弄清楚mysql查询中的错误

3 个答案: