复杂的SQL查询。任何方法来简化？

Question

我正在查询。我有以下表格：

CREATE TABLE #House 
( 
    HouseName Varchar(1), 
    Address Varchar(255) 
) 

CREATE TABLE #Events 
(
    Id Integer, 
    HouseName Varchar(1), 
    EventName Varchar(255), 
    Date Date, 
    Family Varchar(255) 
) 

INSERT #House VALUES('A', '1 Market St') 
INSERT #House VALUES('B', '2 Market St') 
INSERT #House VALUES('X', '3 Market St') 
INSERT #House VALUES('D', '4 Market St') 

INSERT #Events VALUES(1,'A','MoveIn','2005-01-31','Smith') 
INSERT #Events VALUES(2,'A','Remodel','2005-03-31','Smith') 
INSERT #Events VALUES(3,'A','Remodel','2008-03-31','Smith') 
INSERT #Events VALUES(4,'A','CleanUp','2008-05-31','Smith') 
INSERT #Events VALUES(5,'B','MoveIn','2005-01-31','Newton') 
INSERT #Events VALUES(6,'B','MoveOut','2008-05-01','Newton') 
INSERT #Events VALUES(7,'B','MoveIn','2008-12-01','Einstein') 
INSERT #Events VALUES(8,'D','MoveIn','2007-08-31','Soo') 
INSERT #Events VALUES(9,'D','MoveOut','2010-08-13','Soo') 

我希望得到以下结果：

HouseName Address  MostRecentResident MoveInDate 
    A   1 Market  StSmith   2005-01-31 
    B   2 Market St Einstein   2008-12-01 
    D   4 Market St Soo    2007-08-31 

注：楼B有两个MoveIn事件。

这是查询。你认为有更简单的方法来获得相同的结果吗？

Select 
    a.HouseName, a.Address, b.Family as [MostRecentResident], 
    mid.MoveInDate 
from 
    #House a, #Events b, 
    --MoveInDate of the last family: 
    (Select HouseName, Max(MoveInDate) MoveInDate 
    from 
     (Select HouseName, Family, MIN(Date) MoveInDate 
      From #Events 
      Group by HouseName, Family) ff 
    group by HouseName) mid, 
    --Distinct house and the last move in date: 
    (Select HouseName, MAX(Date) LastMoveInDate 
    From #Events 
    Group by HouseName) lmid 
where 
    a.HouseName = b.HouseName 
    and b.HouseName = lmid.HouseName 
    and b.Date = lmid.LastMoveInDate 
    and b.HouseName = mid.HouseName 

Answer 1

我觉得你只是想一些有条件的聚集联接：

select h.housename, h.address, 
     max(case when seqnum = 1 and eventname = 'Movein' then family end) as MostRecentResident, 
     max(case when seqnum = 1 and eventname = 'Movein' then date end) as MoveInDate 
from #house h join 
    (select e.*, 
      row_number() over (partition by e.housename, e.eventname order by date desc) seqnum 
     from #event e 
    ) e 
    on h.housename = e.housename 
group by h.housename,h.address; 

编辑：

以上可以进一步简化为：

select h.housename, h.address, 
     max(case when seqnum = 1 then family end) as MostRecentResident, 
     max(case when seqnum = 1 then date end) as MoveInDate 
from #house h join 
    (select e.*, 
      row_number() over (partition by e.housename, e.eventname order by date desc) seqnum 
     from #event e 
     where eventname = 'Movein' 
    ) e 
    on h.housename = e.housename 
group by h.housename,h.address; 

或邮寄至：

select h.housename, h.address, 
     e.family as MostRecentResident, 
     e.date as MoveInDate 
from #house h outer apply 
    (select top 1 e.* 
     from #event e 
     where e.eventname = 'Movein' and h.housename = e.housename 
    ) e; 

这似乎是最简单的方法。

Answer 2

我认为这是完全不可能像输出

HouseName Address  MostRecentResident MoveInDate 
    A   1 Market  StSmith   2005-01-31 
    B   2 Market St Einstein   2008-12-01 
    D   4 Market St Soo    2007-08-31 

数据集作为MostRecentResident包含StSmith，如果是错字，它应该是史密斯。

那么也许你想

select a.HouseName,a.Address,b.Family as MostRecentResident,b.Date as MoveInDate from #House a 
CROSS APPLY (SELECT TOP(1) Family,Date FROM #Events WHERE EventName='MoveIn' and HouseName=a.HouseName order by Date desc) as b 

应用交叉应用可以简化这个查询。

Answer 3

SELECT * FROM (
    SELECT h.*,e.Family AS MostRecentResident,e.Date AS MoveInDate,ROW_NUMBER()OVER(PARTITION BY h.HouseName ORDER BY e.Date desc) AS rn 
    FROM #House AS h INNER JOIN #Events AS e ON h.HouseName=e.HouseName 
    WHERE e.EventName='MoveIn' 
) AS t WHERE t.rn=1 

 

HouseName Address    MostRecentResident MoveInDate rn 
--------- -------------------- -------------------- ---------- ---------- 
A   1 Market St   Smith    2005-01-31 1 
B   2 Market St   Einstein    2008-12-01 1 
D   4 Market St   Soo     2007-08-31 1