通过代码
SELECT
level,
count('level') level_cnt
FROM
user_info u
WHERE
u.uid in (
SELECT
uid
FROM
exam_record e_r
LEFT JOIN
examination_info e_i
on
e_r.exam_id = e_i.exam_id
WHERE
tag = 'SQL'and
score > 80)
GROUP BY
level
ORDER BY
level_cnt desc;
emm没啥说的很简单,表连接查符合条件的uid,然后筛选对应的level,count就行。
哦对,where in 果然比再套一层select看着舒服
旧知识时间
left join 左边是主表右边是从表
right join 右边是主表,左边是从表