Question

有我的问题：

enter code here

我有一个名为test的表，看起来像这样

id|  service  |   sub service  | Qt  |   date

1 | service_1 | sub_service_11 |  3  | 2011-12-03
2 | service_1 | sub_service_12 |  6  | 2011-12-03
3 | service_1 | sub_service_13 |  4  | 2011-12-03

后来我有一个名为datedim的表，看起来像这样

id|   date 

1 | 2011-12-01
2 | 2011-12-02
3 | 2011-12-03
4 | 2011-12-04
5 | 2011-12-05

我想要做的是，即使没有匹配，每个sub_service也会从datedim返回所有日期。

所以基本上看起来像这样的东西

sub_service_11 | 2011-12-01 | NULL
sub_service_11 | 2011-12-02 | NULL
sub_service_11 | 2011-12-03 | 3
sub_service_11 | 2011-12-04 | NULL
sub_service_11 | 2011-12-05 | NULL
sub_service_12 | 2011-12-01 | NULL
sub_service_12 | 2011-12-02 | NULL
sub_service_12 | 2011-12-03 | 6
sub_service_12 | 2011-12-04 | NULL
sub_service_12 | 2011-12-05 | NULL
sub_service_13 | 2011-12-01 | NULL
sub_service_13 | 2011-12-02 | NULL
sub_service_13 | 2011-12-03 | 4
sub_service_13 | 2011-12-04 | NULL
sub_service_13 | 2011-12-05 | NULL

我确实尝试过RIGHT JOIN，UNIONS和其他东西，但我无法弄明白。

有谁知道我怎么能做到这一点？

谢谢，

Answer 1

这就是你需要的：

select 
  ss.sub_service, 
  dd.date,
  ts.qt
from 
  (datedim dd, (select distinct sub_service from test) ss)
 left join test ts on (dd.date = ts.date and ts.sub_service = ss.sub_service)
order by ss.sub_service, dd.date

Answer 2

由于您有一个包含每个sub_service的表（让我们称之为sub_service_list），您应该能够执行以下操作：

SELECT
s.sub_service, d.date, t.Qt
FROM (sub_service_list s,datedim d) 
LEFT JOIN test t ON s.sub_service=t.sub_service AND d.date=t.date

Answer 3

你可以这样做：

select t.id, sub_service, case when d.date = t.date then qt else null end as qt
from test t cross join datedim d 
order by sub_service, d.date

如何使用JOIN检索所有条目？

3 个答案: