Question

我正在使用Postgres 9.5。我有以下查询，旨在查找我的表中相同的数据行（但唯一的ID）。

select e.name, 
       e.day, 
       e.distance, 
       e.created_at, 
       e2.created_at 
from events e, 
     events e2 
where e.name = e2.name 
  and e.distance = e2.distance 
  and e.day = e2.day 
  and e.web_crawler_id = e2.web_crawler_id 
  and e.id <> e2.id 
  and e.web_crawler_id = 1 
order by e.day desc;

我最终想要删除其中一个重复的行 - 所以可能会删除具有最大“created_at”日期的行。但我不确定如何编写查询只返回两个相同的行之一。我该怎么做？

Answer 1

您可以使用LIMIT：

select e.name, e.day, e.distance, e.created_at, e2.created_at from events e, events e2 where e.name = e2.name and e.distance = e2.distance and e.day = e2.day and e.web_crawler_id = e2.web_crawler_id and e.id <> e2.id and e.web_crawler_id = 1 order by e.day desc LIMIT 1;

Answer 2

有很多方法但是没有更改你的sql，你可以做的比做而不是＆lt;＆gt;对于id：

select e.name, e.day, e.distance, e.created_at, e2.created_at 
from events e, events e2
where e.name = e2.name
and e.distance = e2.distance
and e.day = e2.day 
and e.web_crawler_id = e2.web_crawler_id 
and e.id > e2.id 
and e.web_crawler_id = 1

如何在Postgres中删除我的两个重复数据行之一？

2 个答案: