Question

mysql中如何按条件去重

如有一个表text
id name GRADE
1 zs 25
2 ls 26
3 wq null
4 kj null
5 lk 25
我只想把GRADE列的非null字段去重
得到效果为
id name GRADE
1 zs 25
2 ls 26
3 wq null
4 kj null

Answer 1

利用group by
代码如下：
SELECT * FROM(
select * from customer where user=(
SELECT source_user from customer WHERE user='admin') UNION ALL select * from customer where user=(
select source_user from customer where user=(
SELECT source_user from customer WHERE user='admin')) union ALL select * from customer where user=(
select source_user from customer where user=(
select source_user from customer where user=(
SELECT source_user from customer WHERE user='admin'))) UNION ALL select * from customer where source_user=(/*我的上线的上线的user*/
select user from customer where user=(
select source_user from customer where user=(
SELECT source_user from customer WHERE user='admin'))) union all select * from customer where source_user=(/*我的上线的上线的上线user*/
select user from customer where user=(
select source_user from customer where user=(
select source_user from customer where user=(
SELECT source_user from customer WHERE user='admin'))))) as alias group by user;

Answer 2

直接查出来，通过数组循环，非空的以GRADE为key值，进行重铸数组就可以了。不需要去复杂的查库。

Answer 3

考虑使用union连接两种情况的数据，给个示例：
select id, name, grade from `text` where grade is not null group by grade
union all
select id, name, grade from `text` where grade is null