此查询位于下表
SELECT ID,
Value,
As_of
FROM Table a
INNER JOIN (
SELECT ID,
MAX(As_of) AS As_of
FROM Table
GROUP BY ID
) b
ON a.ID=b.ID
AND a.As_of = b.As_of
表格
ID Value As_of
1173 156 20090601
1173 173 20081201
1173 307 20080901
1173 305 20080601
127 209 20090301
127 103 20081201
127 113 20080901
127 113 20080601
1271 166 20090201
1271 172 20081201
1271 170 20080901
1271 180 20080601
使其看起来像这样
Result
ID Value As_of
1173 156 20090601
127 209 20090301
1271 166 20090201
它获取每个ID的As_of的MAX并返回...(来自stackoverflow上的另一个Question)
我基本上有相同的表,但不是“物理表”,而是查询结果:
查询:
SELECT tblClassificationHistory.inmateID,
tblClassificationHistory.classificationID
FROM tblinmate
INNER JOIN tblClassificationHistory
ON tblinmate.inmateID = tblClassificationHistory.inmateID
GROUP BY tblClassificationHistory.inmateID,
tblClassificationHistory.classificationID,
tblClassificationHistory.reclassificationDate
ORDER BY tblClassificationHistory.inmateID;
产生此结果:
inmateID classificationID reclassificationDate
2 3 9/22/2015
2 4 9/13/2015
2 8 9/8/2015
3 8 9/13/2015
4 4 9/15/2015
4 8 6/16/2015
5 3 9/15/2015
5 4 9/16/2015
5 8 7/7/2015
6 8 9/14/2015
7 7 9/13/2015
8 3 8/4/2015
8 8 6/1/2015
9 3 9/15/2015
10 6 9/13/2015
11 3 9/13/2015
12 3 8/3/2015
12 4 9/9/2015
12 6 9/13/2015
12 8 7/6/2015
13 8 9/13/2015
14 8 9/13/2015
15 4 9/13/2015
16 4 9/13/2015
17 8 9/14/2015
18 8 9/14/2015
19 3 9/15/2015
我想在我的脑海中使用“他的”查询,但几个小时后我就不能......我猜它是一个子查询......但我不能为我的生活得到正确的语法......
结果我之后:每个inmateID的上次日期的分类ID
inmateID classificationID reclassificationDate
2 3 9/22/2015
3 8 9/13/2015
4 4 9/15/2015
5 4 9/16/2015
6 8 9/14/2015
7 7 9/13/2015
8 3 8/4/2015
9 3 9/15/2015
10 6 9/13/2015
11 3 9/13/2015
12 6 9/13/2015
13 8 9/13/2015
14 8 9/13/2015
15 4 9/13/2015
16 4 9/13/2015
17 8 9/14/2015
18 8 9/14/2015
19 3 9/15/2015
答案 0 :(得分:2)
SELECT a.inmateID,
a.classificationID,
b.max_date
FROM (
SELECT tblClassificationHistory.inmateID,
tblClassificationHistory.classificationID,
tblClassificationHistory.reclassificationDate
FROM tblinmate
INNER JOIN tblClassificationHistory
ON tblinmate.inmateID = tblClassificationHistory.inmateID
) a
INNER JOIN (
SELECT tblClassificationHistory.inmateID,
MAX(tblClassificationHistory.reclassificationDate) as max_date
FROM tblinmate
INNER JOIN tblClassificationHistory
ON tblinmate.inmateID = tblClassificationHistory.inmateID
GROUP BY tblClassificationHistory.inmateID
) b
ON a.inmateID = b.inmateID
AND a.reclassificationDate = b.max_date
ORDER BY a.inmateID;
您可以将其细分为两个子查询(a
和b
)。在b
中,我们会在表格中找到MAX日期,不包括classificationID,只能通过inmateID进行分组。我们最后得到一张这样的表:
+----------+-----------+
| inmateID | max_date |
+----------+-----------+
| 2 | 9/22/2015 |
| 3 | 9/13/2015 |
| 4 | 9/15/2015 |
| 5 | 9/16/2015 |
| 6 | 9/14/2015 |
| 7 | 9/13/2015 |
| ... | ... |
+----------+-----------+
在a
中,我们只是抓取未聚合的值,包括此复发的分类ID:
+----------+------------------+----------------------+
| inmateID | classificationID | reclassificationDate |
+----------+------------------+----------------------+
| 2 | 3 | 9/22/2015 |
| 2 | 4 | 9/13/2015 |
| 2 | 8 | 9/15/2015 |
| 3 | 8 | 9/16/2015 |
| 4 | 4 | 9/14/2015 |
| 4 | 8 | 9/13/2015 |
| ... | ... | ... |
+----------+------------------+----------------------+
我们加入两个子查询,在a
中查找行,其中reclassificationDate等于MAX日期,刚刚在b
中计算。然后,我们可以从那些连接的行中获取适当的分类ID来构建我们的最终表格。