我有一张表格
id_customer__ | status | time_stmpd_at | idx
---------------+-----------------------+-----------------------+-----
112220 | enabled____________at | 2017-12-13 16:12:42.0 | 1
112220 | sale_locked_at__ | 2017-12-13 14:52:43.0 | 2
112220 | qual_sale_at | 2017-12-06 12:22:50.0 | 3
112220 | quality_control___at | 2017-11-28 18:22:02.0 | 4
112220 | returned__at | 2017-10-12 23:02:41.0 | 5
我希望status idx = 2和time_stmpd_at，其中idx = 1.并且能够为所有客户ID执行此操作。
我试图将条件放入select语句中，如下所示：
select
id_customer__,
if(idx=2, status, NULL) as previous_status,
if(idx=1, time_stmpd_at, NULL) as time_stmpd_at
from htable
但这让我失望
id_customer__ | previous_status | time_stmpd_at
---------------+------------------+-----------------------
119650 | NULL | 2017-12-13 16:12:42.0
119650 | sale_locked_at__ | NULL
119650 | NULL | NULL
119650 | NULL | NULL
119650 | NULL | NULL
接下来，我必须将该字段合并为一行。但我觉得必须有更好的方法。有关整体方法的任何建议吗？
答案 0 :(得分：3)
您可以使用条件聚合执行此操作。
select
id_customer__,
max(case when idx=2 then status end) as previous_status,
max(case when idx=1 then time_stmpd_at end) as time_stmpd_at
from htable
group by id_customer__
答案 1 :(得分：1)
您可以使用MAX并将表格限制为只有您想要的索引（您不必这样做但是为什么还要计算不相关的行）：
SELECT id_customer__,
MAX(CASE WHEN idx=1 THEN time_stmpd_at ELSE NULL END) time_stmpd_at,
MAX(CASE WHEN idx=2 THEN status ELSE NULL END) status
FROM htable
WHERE idx IN (1,2)
GROUP BY id_customer__
或者您可以单独提取这些索引并在id_customer__
SELECT h1.id_customer__, h1.time_stmpd_at , h2.status
FROM
(SELECT * FROM htable WHERE idx=1) h1 INNER JOIN
(SELECT * FROM htable WHERE idx=2) h2 ON h1.id_customer__ = h2.id_customer__
答案 2 :(得分：0)
（基于@VamsiPrabhala的回答，但改为使用arbitrary聚合）
我建议使用arbitrary聚合（而不是max），因为它更能传达意义：
select id_customer,
arbitrary(status) filter(where idx=2) as previous_status,
arbitrary(time_stmpd_at) filter(where idx=1) as time_stmpd_at
from htable
group by id_customer
使用arbitrary有两个原因：
arbitrary表示您没有进行任何max聚合（如果以后有人会阅读此查询，这很好）arbitrary