Question

我有两个类似的表：

表1 - 唯一ID＆＃39;

ID     Date
1      3/8/2017
2      3/8/2017
3      3/8/2017

表2

ID     Date          SourceID
1      3/8/2017      1
1      3/8/2017      2
1      3/8/2017      3
2      3/8/2017      2
3      3/8/2017      1
3      3/8/2017      3

我想编写一个结果如下的查询：

结果

ID     SourceID
1      2
2      2
3      1

源ID排序应为2,1,3

我有：

select Table1.ID
    , COALESCE(Join1.SourceID, Join2.SourceID, Join3.SourceID) as SourceID
from Table1
left outer join Table2 Join1
    on Table1.date = Join1.date
        and Table1.ID = Join1.ID
        and Join1.SourceID = 2
left outer join Table2 Join2
    on Table1.date = Join2.date
        and Table1.ID = Join2.ID
        and Join2.SourceID = 1
        and Join1.SourceID is null
left outer join Table2 Join3
    on Table1.date = Join3.date
        and Table1.ID = Join3.ID
        and Join3.SourceID = 3
        and Join1.SourceID is null
        and Join2.SourceID is null

但目前这只是将记录保存在sourceid = 2并且不会添加到其他源代码中。

提前感谢您的帮助。如果您需要任何澄清，请告诉我。使用SQL-Server。我只需要一些固定数量的源，所以我避免使用游标。

Answer 1

这是优先级查询。我会用outer apply：

来做

select t1.*, t2.sourceId
from table1 t1 outer apply
     (select top 1 t2.*
      from table2 t2
      where t2.id = t1.id and t2.date = t1.date
      order by (case t2.sourceid when 2 then 1 when 1 then 2 when 3 then 3 end)
     ) t2;

注意：为了便于阅读，您可以将order by简化为：

order by charindex(cast(t2.sourceId as varchar(255)), '2,1,3')

如果您对outer apply感到不舒服，可以使用一个join做同样的事情：

select t1.*, t2.sourceId
from table1 t1 join
     (select t2.*,
             row_number() over (partition by id, date
                                order by (case t2.sourceid when 2 then 1 when 1 then 2 when 3 then 3 end)
                               ) as seqnum
      from table2 t2
     ) t2
     on t2.id = t1.id and t2.date = t1.date and t2.seqnum = 1;

瀑布加入条件

1 个答案: