Question

我的表格如下：

ID - USER  - LOCATION
1  - Steve - home
2  - Steve - work
3  - Steve - school
4  - Eve   - home
5  - Eve   - work
6  - Eve   - school
7  - RJ    - school
etc.

如何从所有用户那里获得两个职位？

修改

输出应为：

ID - USER  - LOCATION
1  - Steve - home
2  - Steve - work
4  - Eve   - home
5  - Eve   - work
7  - RJ    - school

Answer 1

SELECT x.*
  FROM my_table x 
  JOIN my_table y 
    ON y.user = x.user 
   AND y.id <= x.id 
 GROUP 
    BY x.id 
HAVING COUNT(*) <=2;
+----+-------+----------+
| ID | USER  | LOCATION |
+----+-------+----------+
|  1 | Steve | home     |
|  2 | Steve | work     |
|  4 | Eve   | home     |
|  5 | Eve   | work     |
|  7 | RJ    | school   | 
+----+-------+----------+

E.g：

submit

Answer 2

类似的东西：

public static void Main(string[] args) { ... }

或者，如果您想要2个特定位置：

SELECT a.USER
FROM YourTable a
WHERE LOCATION IN (
                   SELECT DISTINCT(b.LOCATION)
                   FROM YourTable b
                   WHERE USER = a.USER
                   LIMIT 2
                   )

编辑：

似乎MySql（或某些版本）不接受SELECT USER FROM YourTable WHERE LOCATION = 'home' OR LOCATION = 'work'进入子查询

为每个值选择两行

2 个答案: