mysql中重复数据只取条

select * from table_a where id in (select min(id) from table_a group by a)

 

 

select * from altals where id in (select min(id) from altals group by SUBSTRING_INDEX(cids,',',1))

 

 

SUBSTRING_INDEX(cids,',',1))截取字符串

group by 按照什么分组

select min(id) from table_a group by a  根据a来分组找出最小的id