Question

表格：

|A    |    |B          |    |C                               |
|-----|    |-----|-----|    |-----|-----|-----------|--------|
|AKey |    |BKey |AKey |    |CKey |BKey |Date       |Result  |
|-----|    |-----|-----|    |-----|-----|-----------|--------|
|1    |    |1    |1    |    |101  |1    |2016-12-01 |F       |
|     |    |2    |1    |    |102  |1    |2016-12-01 |F       |
|     |    |3    |1    |    |103  |3    |2016-12-01 |P       |
|     |    |     |     |    |104  |1    |2016-12-01 |P       |

我试过这个SQL命令：

SELECT a.Akey, b.BKey, c.CKey, Date, Result
FROM A AS a
INNER JOIN B as b ON a.AKey=b.AKey
LEFT JOIN (SELECT * FROM C WHERE Date="2016-12-01"
ORDER BY CKey DESC
LIMIT 0, 1) AS c ON c.BKey=b.BKey
WHERE a.AKey=1

我得到的结果如下：

|AKey |BKey |CKey |Date       |Result  |
|-----|-----|-----|-----------|--------|
|1    |1    |104  |2016-12-01 |P       |
|1    |2    |NULL |NULL       |NULL    |
|1    |3    |NULL |NULL       |NULL    |

但是，如何得到如下结果？

|AKey |BKey |CKey |Date       |Result  |
|-----|-----|-----|-----------|--------|
|1    |1    |101  |2016-12-01 |P       |
|1    |2    |NULL |NULL       |NULL    |
|1    |3    |103  |2016-12-01 |P       |

Answer 1

你可能想要这样的东西：

GROUP BY

您必须使用CKey子句才能获得每BKey的最小C值。然后加入{{1}}表格以获得更多其他字段。

Answer 2

您的内部查询始终选择相同的行。您可以使用Akey

获取每个NOT EXISTS()的最新记录

SELECT a.Akey, b.BKey, c.CKey, Date, Result 
FROM A AS a
INNER JOIN B as b ON a.AKey=b.AKey 
LEFT JOIN (SELECT * 
            FROM C 
            WHERE Date="2016-12-01" 
             AND NOT EXISTS(SELECT 1 FROM c t1
                            WHERE t1.cid > c.cid 
                              and t1.bkey = c.bkey) ) AS c 
ON c.BKey=b.BKey 
WHERE a.AKey=1

在MYSQL中选择INNER JOIN SELECT

2 个答案: