三表连表查询+groupby怎么做

Question

a b c
a.pid =b.pid
b.prov=c.pid

groupby a.moon

Answer 1

比如
SELECT t2.group_id,count(*) as gnm from A t1 LEFT JOIN B t2 on t1.id=t2.id LEFT JOIN C t3 on t2.id=t3.id
GROUP BY t2.group_id。
执行逻辑就是先查询，再GROUP BY
主要你要搞清楚group by 后多个参数的含义。