Question

这是一个测试表

mysql> select * from test;
+----+---------+----------+
| id | content | content2 |
+----+---------+----------+
| 12 | a       | 1        |
| 13 | a       | 2        |
| 14 | a       | 3        |
| 15 | a       | 10       |
| 16 | a       | 11       |
| 17 | a       | 12       |
+----+---------+----------+
6 rows in set (0.00 sec)

我希望得到像这样的记录

+----+---------+------+------+
| id | content | a    | b    |
+----+---------+------+------+
| 12 | a       | 3    | 12   |
+----+---------+------+------+

我想获得一条记录，选择不在所有数据中的东西

这是假代码：

mysql> select content,max(content2 where content2 < 5 oder by content2 DESC) AS a,
       max(content2 where content2 < 15 oder by content2 DESC) AS b
       from test
       group by content

Answer 1

drop table if exists t;
create table t(id int,  content varchar(1), content2 int);
insert into t values
( 12 , 'a'       , 1  ),
( 13 , 'a'       , 2  ),
( 14 , 'a'       , 3  ),
( 15 , 'a'       , 10 ),
( 16 , 'a'       , 11 ),
( 17 , 'a'       , 12 );

select min(id) id ,content, 
        max(case when content2 < 5 then content2 else null end) a,
        (select max(case when t2.content2 < 15 then t2.content2 else null end) 
        from t t2 where t2.content = t.content group by t2.content) b
from t
group by content

+------+---------+------+------+
| id   | content | a    | b    |
+------+---------+------+------+
|   12 | a       |    3 |   12 |
+------+---------+------+------+
1 row in set (0.00 sec)

有没有办法在mysql中选择具有条件和顺序条件的字段

1 个答案: