Question

下表包含活动及其任务：

TASK_ID | TASK_NAME | ACT_ID
========+===========+=======
1000    | A         | 300
1001    | B         | 300
1002    | C         | 300
1003    | A         | 400
1004    | D         | 400
1005    | B         | 500
1006    | C         | 500
1007    | D         | 500
1008    | A         | 600

我需要一个SQL查询，它将以关键形式表示活动及其第一和第二个任务。结果应如下所示：

ACT_ID | Task1st | Task2nd
=======+=========+========
300    | A       | B
400    | A       | D
500    | B       | C
600    | A       | NULL

Answer 1

使用以下带有数据透视的查询

select * from
    (
    select act_id,task_name,rn from 
    (
    select distinct act_id,task_name,row_number() over (partition by act_id order by act_id) rn from table1 
    ) where rn<=2
    )
    pivot
    (
    min(task_name) as task for rn in ( 1  ,2  )
    )
    order by act_id

Answer 2

SELECT a.ACT_ID, a.TASK_NAME, b.TASK_NAME
FROM activities a
LEFT JOIN activities b
ON ( a.ACT_ID = b.ACT_ID
     AND b.TASK_ID > a.TASK_ID
     AND NOT EXISTS ( SELECT 'y'
                      FROM activities b2
                      WHERE b2.ACT_ID = b.ACT_ID
                      AND b2.TASK_ID > a.TASK_ID 
                      AND b2.TASK_ID < b.TASK_ID 
                     )
    )
WHERE NOT EXISTS ( SELECT 'x'
                   FROM activities a2
                   WHERE a2.ACT_ID = a.ACT_ID
                   AND a2.TASK_ID < a.TASK_ID 
                  )

如果你需要一个ansi-sql查询可以尝试这个。附：我没有尝试过数据让我知道它是否有效。

第一组和第二组来自组

2 个答案: