更新查询与条件在SQL

Question

我有了2列的表，我试图更新基于这些标准的另一个表：

1. 设置标志，以“好”在最重复键对于同一GROUP_KEY Main_Key列（请注意，我们可以有任何GROUP_KEY不同Main_Keys）
2. 设置标志，以“坏”在Main_Key列中至少重复键为同一GROUP_KEY
3. 设置标志，以“唐” t使用'如果不同的Main_Keys对于相同的GROUP_KEY是相等的

这里是我的表

GROUP_KEY MAIN_KEY 
22   4 
22   4 
22   55 
22   55 
22   55 
22   55 
10   10 
10   10 
18   87 
18   22 
18   22 

这里是预期结果的UPDATE

GROUP_KEY MAIN_KEY   FLAG 
    22   4   Bad 
    22   4   bad 
    22   55   Good 
    22   55   Good 
    22   55   Good 
    22   55   Good 
    10   10   Don't Use 
    10   10   Don't Use 
    18   87   Bad 
    18   22   Good 
    18   22   Good 

后，我只知道怎么做只是正常的更新查询，但没有，甚至开始这个逻辑。日Thnx的帮助

Answer 1

用途：

declare @t table(GROUP_KEY int, MAIN_KEY int) 

insert @t values 
(22, 4), 
(22, 4), 
(22, 55), 
(22, 55), 
(22, 55), 
(22, 55), 
(10, 10), 
(10, 10), 
(18, 87), 
(18, 22), 
(18, 22) 

select t.*, b.flag 
from @t t 
join 
(
    select a.GROUP_KEY, a.MAIN_KEY 
     , 
      case 
       when a.GROUP_KEY = a.MAIN_KEY 
        then 'Don''t Use' 
       when a.count = MAX(a.count) over(partition by a.GROUP_KEY) 
        then 'Good' 
       else 'Bad' 
      end [flag] 
    from 
    (
     select t.GROUP_KEY, t.MAIN_KEY, COUNT(*) [count] 
     from @t t 
     group by t.GROUP_KEY, t.MAIN_KEY 
    )a 
)b 
on b.GROUP_KEY = t.GROUP_KEY and b.MAIN_KEY = t.MAIN_KEY 

输出：

GROUP_KEY MAIN_KEY flag 
----------- ----------- --------- 
10   10   Don't Use 
10   10   Don't Use 
18   22   Good 
18   22   Good 
18   87   Bad 
22   4   Bad 
22   4   Bad 
22   55   Good 
22   55   Good 
22   55   Good 
22   55   Good 

更新： 假设你有你的表flag列：

update @t 
set flag = b.flag 
from @t t 
join 
(
    select a.GROUP_KEY, a.MAIN_KEY 
     , 
      case 
       when a.GROUP_KEY = a.MAIN_KEY 
        then 'Don''t Use' 
       when a.count = MAX(a.count) over(partition by a.GROUP_KEY) 
        then 'Good' 
       else 'Bad' 
      end [flag] 
    from 
    (
     select t.GROUP_KEY, t.MAIN_KEY, COUNT(*) [count] 
     from @t t 
     group by t.GROUP_KEY, t.MAIN_KEY 
    )a 
)b 
on b.GROUP_KEY = t.GROUP_KEY and b.MAIN_KEY = t.MAIN_KEY