GROUP_CONCAT聚合函数inner join关联空表之后，查询有值

聚合函数group_concat要跟随group by，不然就会导致一下场景：
b表为空表，按理说查询出来结果应该为0
select count() from (SELECT a.,GROUP_CONCAT(b.nickname SEPARATOR ‘,’) user a
INNER JOIN b on a.uid=b.uid where b.state=‘0’ )x
但是查询出来的结果会是1，而如果跟上group by之后就正确了
select count() from (SELECT a.,GROUP_CONCAT(b.nickname SEPARATOR ‘,’) user a
INNER JOIN b on a.uid=b.uid where b.state=‘0’ group by uid)x