Question

Table_01：

----------------
ROW_ID | NAME   
----------------
11223  | Frank      
11224  | Frank
11225  | James
11226  | James
11227  | Joe
11228  | Joe
11229  | Joe
11230  | Tom
11231  | Tom
11232  | Tom

Table_02：

--------------------------------------------------
ROW_ID | NAME   | EVENT_DATE    | EVENT_LOCATION
--------------------------------------------------
11106  | Frank  | 27/01/2017    | London
11109  | Frank  | 19/01/2017    | Munich
11105  | James  | 27/01/2017    | New York
11110  | James  | 02/01/2017    | L.A
11101  | Joe    | 27/01/2017    | Paris
11104  | Joe    | 26/01/2017    | Barcelona
11107  | Joe    | 31/01/2017    | Tokyo
11102  | Tom    | 24/01/2017    | Prague
11103  | Tom    | 03/01/2017    | Lisbon
11108  | Tom    | 20/01/2017    | Dublin

我想为不同的用户查询 Table_01 ，并从 Table_02

了解他们最近的EVENT_DATE和EVENT_LOCATION

答案：

---------------------------------------------------
NAME    | NAME    | EVENT_DATE   | EVENT_LOCATION
---------------------------------------------------
Frank   | Frank   | 27/01/2017   | London
James   | James   | 27/01/2017   | New York
Joe     | Joe     | 31/01/2017   | Tokyo
Tom     | Tom     | 24/01/2017   | Prague

Microsoft SQL Server 2016.兼容级别：SQL Server 2005（90）

Answer 1

您可以使用row_number()：

执行此操作

select t2.*
from (select distinct name from table_01) n join
     (select t2.*, 
             row_number() over (partition by name order by event_date desc) as seqnum
      from table_02 t2
     ) t2
     on n.name = t2.name and t2.seqnum = 1.

除非您想要进行过滤，否则您似乎真的不需要table_01：

select t2.*
from (select t2.*, 
             row_number() over (partition by name order by event_date desc) as seqnum
      from table_02 t2
     ) t2
where t2.seqnum = 1.

Answer 2

除了on name之外，我没有看到两个表如何加入。

有很多方法可以做到这一点。以下是其中一些：

with common_table_expression as ()使用 row_number()

with cte as (
  select  u.Name, e.Event_Date, e.Event_Location
      , rn = row_number() over (
              partition by u.Name
              order by e.[Event_Date] desc
            )
    from (select distinct Name from table_01) u
      left join table_02 e
        on u.Name = e.Name
)
select Name, Event_Location, Event_Date
  from cte
  where rn = 1

子查询而不是cte：

select Name, Event_Location, Event_Date
from (
  select  u.Name, e.Event_Date, e.Event_Location
      , rn = row_number() over (
              partition by u.Name
              order by e.[Event_Date] desc
            )
    from (select distinct Name from table_01) u
      left join table_02 e
        on u.Name = e.Name
  ) as sub
where rn = 1

cross apply 版本：

 select distinct
     u.Name
   , e.Event_Location
   , e.[Event_Date]
  from (select distinct Name from table_01) u
    cross apply (
      select top 1
            Event_Date
          , Event_Location
        from table_02 e
        where e.Name =u.Name
        order by e.Event_Date desc
       ) as e;

top with ties 版本：

select top 1 with ties
    u.Name, e.Event_Date, e.Event_Location
from (select distinct Name from table_01) u
  left join table_02 e
    on u.Name = e.Name
  order by 
    row_number() over (
      partition by u.Name
          order by e.Event_Date desc
      )

从一个表中选择不同的用户，在其他表

2 个答案: