我是新的 Sql 查询。我想从两个表的差异中创建一个表。
这是我的查询:
SELECT * FROM `question` WHERE `relatedFields` = 'Math' LEFT JOIN `answer` ON `question`.ques = `answer`.ques where `answer`.TeacherNumber=1111111111
请帮忙。
最佳答案
将第一个 WHERE
子句移动到末尾,并将另一个 where 条件移动到 ON
以获得 true LEFT JOIN
:
SELECT *
FROM `question`
LEFT JOIN `answer` ON `question`.ques = `answer`.ques
and `answer`.TeacherNumber=1111111111
where `question`.relatedFields = 'Math'
替代语法:
SELECT *
FROM
(select * from `question` WHERE `relatedFields` = 'Math') as q
LEFT JOIN
(select * from `answer` where TeacherNumber = 1111111111) as a
ON q.ques = a.ques
关于MySql 查询 : Left Join,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32564140/