Question

我想获得一个活动的所有舞台，课程，状态。问题是某些阶段有几行：

mysql> select stage,class,status from results where event=3009 and person=81451;
+-------+-------+-----------+
| stage | class | status    |
+-------+-------+-----------+
|  3210 | 52800 | OK        |
|  3209 | 52800 | Cancelled |
|  3208 | 52800 | OK        |
|  3209 | 52798 | OK        |
+-------+-------+-----------+
4 rows in set (0,01 sec)

每个阶段我只想要一行。所以我的想法是使用group by：

mysql> select stage,class,status from results where event=3009 and person=81451 group by stage;
+-------+-------+-----------+
| stage | class | status    |
+-------+-------+-----------+
|  3208 | 52800 | OK        |
|  3209 | 52800 | Cancelled |
|  3210 | 52800 | OK        |
+-------+-------+-----------+
3 rows in set (0,00 sec)

但是在多行的情况下，我希望选择status = OK行。我怎么能这样做？

我想要最终得到的结果是：

+-------+-------+-----------+
| stage | class | status    |
+-------+-------+-----------+
|  3208 | 52800 | OK        |
|  3209 | 52798 | OK        |
|  3210 | 52800 | OK        |
+-------+-------+-----------+

Answer 1

由于OK大于CANCELLED，您可以使用MAX()。

SELECT  a.*
FROM    results a
        INNER JOIN
        (
            SELECT  stage, MAX(status) status
            FROM    result
            WHERE   event = 3009 
                    AND person = 81451
            GROUP   BY stage
        ) b ON  a.stage = b.stage AND
                a.status = b.status

SQLFiddle Demo

如何按行为控制组？

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