[英]SQL Select only rows with Max Value on a Column FILTERED by Column
这是优秀答案的后续问题:
SQL仅选择列上具有最大值的行
SQLFiddle http://sqlfiddle.com/#!2/3077f/2
表“你的表”:
| id | val | ignore | content |
-------------------------------
| 1 | 10 | 0 | A |
| 1 | 20 | 0 | B |
| 1 | 30 | 1 | C |
| 2 | 40 | 0 | D |
| 2 | 50 | 0 | E |
| 2 | 60 | 1 | F |
在查找每个 id 的最大 val 时,使用以下 sql:
select yt1.*
from yourtable yt1
left outer join yourtable yt2
on (yt1.id = yt2.id and yt1.val < yt2.val )
where yt2.id is null;
所以结果将是在这种情况下
| id | val | ignore | content |
-------------------------------
| 1 | 30 | 1 | C |
| 2 | 60 | 1 | F |
问题是如何在列“忽略”为 =1 时过滤掉它,因此结果将是
| id | val | ignore | content |
-------------------------------
| 1 | 20 | 0 | B |
| 2 | 50 | 0 | E |
您需要将条件同时放在子查询和外部查询中:
select yt1.*
from yourtable yt1 left outer join
yourtable yt2
on yt1.id = yt2.id and yt1.val < yt2.val and yt2.ignore <> 1
where yt2.id is null and yt1.ignore <> 1;
您可以简单地添加另一个条件and yt1.ignore <> 1
,如下所示:
select yt1.*
from yourtable yt1
left outer join yourtable yt2
on (yt1.id = yt2.id and yt1.val < yt2.val )
where yt2.id is null and yt1.ignore <> 1;
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