left join联合的时候去重

SELECT * from t_ss;

SELECT * from t_kk;

SELECT * from t_ss s LEFT JOIN t_kk k on s.id=k.sid

使用group by去重
SELECT * from t_ss s LEFT JOIN t_kk k on s.id=k.sid GROUP BY k.sid;

或者
SELECT * from t_ss s LEFT JOIN t_kk k on s.id=k.sid GROUP BY s.id;

如果要去重，统计数量，就用DISTINCT
SELECT count(DISTINCT s.id) from t_ss s LEFT JOIN t_kk k on s.id=k.sid