2

可以有多个 Config_RecID，但我只想显示附加到 SR_Service_RecID 的第一个，或者当为空时为 NULL。

SELECT s.SR_Service_RecID
     , sc.Config_RecID

  FROM SR_Service s
       LEFT JOIN SR_Config sc
              ON sc.SR_Service_RecID = s.SR_Service_RecID

 WHERE (sc.Config_RecID = 
       (
           SELECT TOP 1 sc.Config_RecID
             FROM SR_Config sc 
            WHERE sc.SR_Service_RecID = s.SR_Service_RecID
       ) 
       OR sc.Config_RecID IS NULL)

有没有更好/更整洁的方法来做到这一点，还是我走在正确的轨道上？

4

4 回答 4

2

您可以将条件移动到ON子句中：

SELECT s.SR_Service_RecID
     , sc.Config_RecID
FROM SR_Service s
LEFT JOIN SR_Config sc
     ON sc.SR_Service_RecID = s.SR_Service_RecID
     AND sc.Config_RecID = (
           SELECT TOP 1 Config_RecID
           FROM SR_Config sc2 
           WHERE sc2.SR_Service_RecID = s.SR_Service_RecID
     )

这样你就不需要额外的检查sc.Config_RecID IS NULL

于 2013-01-07T01:04:12.187 回答
0 
with Config_RecIDs as (
   select SR_Service_RecID
      , Config_RecID
      , row_number() over (partition by SR_Service_RecID order by Config_RecID) as [rn]
   from SR_Config
)
select sc.SR_Service_RecID, c.Config_RecID
from SR_Config as sc
left join Config_RecIDs as s
   on s.SR_Service_RecID = c.SR_Service_RecID
   and [rn] = 1
于 2013-01-07T02:01:10.773 回答
0

这就是你所追求的吗？

;WITH SR_ConfigCTE AS
(
    SELECT DISTINCT 
         SR_Service_RecID
        ,Config_RecID
    FROM SR_Config
)
SELECT   s.SR_Service_RecID
        ,sc.Config_RecID
FROM SR_Service     s
LEFT 
JOIN SR_ConfigCTE   sc ON sc.SR_Service_RecID = s.SR_Service_RecID
于 2013-01-07T04:50:48.127 回答
0

如果您使用的是 TOP N，那么您就走错了路。它是非标准的和不确定的。

相反，你想要第一个……东西。用 找到它min()。加入或使用相关的子查询。

我不太了解您的查询，但这是一个更简单的查询，它为每种类型提供了名字：

select type, usertype, cast(name as varchar(30)) as name 
from systypes as t
where exists 
      ( select 1 from systypes 
        group by type 
        having min(name) = t.name 
        and type = t.type 
) 
order by type

这产生：

 type usertype name                          
 ---- -------- ------------------------------
    0        0 xml                           
   34       20 image                         
   35        0 ntext                         
   37        0 uniqueidentifier              
   39        0 nvarchar                      
   45        3 binary                        
   47        1 char                          
   48        5 tinyint                       
   50       16 bit                           
   52        6 smallint                      
   55       24 decimal                       
   56        7 int                           
   58       22 smalldatetime                 
   59       23 real                          
   60       11 money                         
   61       12 datetime                      
   62        8 float                         
   63        0 bigint                        
  122       21 smallmoney
于 2013-01-09T08:35:14.563 回答