这个问题与我最近here提供的答案有关。
使用MS Access 2007。
假设我有一个名为mytable
的表,该表由三个字段组成:
id
长整数自动编号(PK)type
文字num
长整数具有以下示例数据:
+----+------+-----+
| id | type | num |
+----+------+-----+
| 1 | A | 10 |
| 2 | A | 20 |
| 3 | A | 30 |
| 4 | B | 40 |
| 5 | B | 50 |
| 6 | B | 60 |
| 7 | C | 70 |
| 8 | C | 80 |
| 9 | C | 90 |
| 10 | D | 100 |
+----+------+-----+
类似于链接的答案,我想输出三个字段,每个type
值的运行总计,运行总计的值限制为最大100
,我可能使用相关的子查询,如下所示:
select q.* from
(
select t.id, t.type, t.num,
(
select sum(u.num)
from mytable u where u.type = t.type and u.id <= t.id
) as rt
from mytable t
) q
where q.rt < 100
这将产生预期的结果:
+----+------+-----+----+
| id | type | num | rt |
+----+------+-----+----+
| 1 | A | 10 | 10 |
| 2 | A | 20 | 30 |
| 3 | A | 30 | 60 |
| 4 | B | 40 | 40 |
| 5 | B | 50 | 90 |
| 7 | C | 70 | 70 |
+----+------+-----+----+
现在假设我希望过滤结果以仅显示type like "[AB]"
的那些值。
如果我使用以下任一查询:
select q.* from
(
select t.id, t.type, t.num,
(
select sum(u.num)
from mytable u where u.type = t.type and u.id <= t.id
) as rt
from mytable t
where t.type like "[AB]"
) q
where q.rt < 100
select q.* from
(
select t.id, t.type, t.num,
(
select sum(u.num)
from mytable u where u.type = t.type and u.id <= t.id
) as rt
from mytable t
) q
where q.rt < 100 and q.type like "[AB]"
结果将按预期进行过滤,但是rt
(运行总计)列中的值消失了:
+----+------+-----+----+
| id | type | num | rt |
+----+------+-----+----+
| 1 | A | 10 | |
| 2 | A | 20 | |
| 3 | A | 30 | |
| 4 | B | 40 | |
| 5 | B | 50 | |
+----+------+-----+----+
为什么过滤器会使相关子查询返回的值消失?
感谢您阅读我的问题的时间,并感谢您提供任何建议。