从2个表，他们延长了行

Question

我的问题选择数据是这样的：

我有两个表。一个携带真实数据，另一个用作备份。每当真实数据发生变化时，触发器会将原始行复制到备份表中。

我需要的是以下几点：

我想选择所有的原始真实数据。这意味着真实数据表中所有从未更改的条目以及第一次插入的备份表中的所有数据。

想象这些表：

╔════════╦══════════╗ ╔══════════╦════════╦══════════╗ 
║ RealId ║ Numeric ║ ║ BackupId ║ RealId ║ Numeric ║ 
╠════════╬══════════╣ ╠══════════╬════════╬══════════╣ 
║  1 ║  3 ║ ║  1 ║  1 ║  7 ║ 
║  2 ║  19 ║ ║  2 ║  1 ║  9 ║ 
║  3 ║  24 ║ ║  3 ║  1 ║  14 ║ 
║  4 ║  5 ║ ║  4 ║  2 ║  2 ║ 
║  5 ║  23 ║ ║  5 ║  3 ║  13 ║ 
╚════════╩══════════╝ ║  6 ║  5 ║  9 ║ 
         ║  7 ║  5 ║  4 ║ 
         ╚══════════╩════════╩══════════╝ 

我的目标是做一个查询，将返回这样的事情：

╔══════════╦════════╦══════════╗ 
║ BackupId ║ RealId ║ Numeric ║ 
╠══════════╬════════╬══════════╣ 
║ 1  ║  1 ║  7 ║ 
║ 4  ║  2 ║  2 ║ 
║ 5  ║  3 ║  13 ║ 
║ NULL  ║  4 ║  5 ║ 
║ 6  ║  5 ║  9 ║ 
╚══════════╩════════╩══════════╝ 

正如你所看到的，我一直想回到做出的第一项与备份表中的特定Realid进行比较。 （RealId和BACKUPID始终是唯一的）

一种方法我想到了

SELECT MIN(BackupId), RealId 
FROM BackupTable 
GROUP BY RealId 

至于真正的表，我想过像

SELECT * 
FROM real-table A 
WHERE NOT EXISTS (
    SELECT * 
    FROM backup-table B 
    WHERE B.RealId = A.RealId 
) 

但我根本无法想想合并表格的正确方法。

Answer 1

使用窗口功能：

Create table #Real (RealID int, [Numeric] int) 

Create table #Backup (BackupID int, RealID int, [Numeric] int) 

Insert into #Real values(1, 3) 
Insert into #Real values(2, 19) 
Insert into #Real values(3, 24) 
Insert into #Real values(4, 5) 
Insert into #Real values(5, 23) 

Insert into #Backup values (1, 1, 7) 
Insert into #Backup values (2, 1, 9) 
Insert into #Backup values (3, 1, 14) 
Insert into #Backup values (4, 2, 2) 
Insert into #Backup values (5, 3, 13) 
Insert into #Backup values (6, 5, 9) 
Insert into #Backup values (7, 5, 4) 

Select distinct 
First_Value(b.[BackupID]) over (partition by r.RealID order by b.BackupID) as [BackupID] 
    , r.RealID as [RealID] 
    , isnull(First_Value(b.[Numeric]) over (partition by r.RealID order by b.BackupID), r.numeric) as [Numeric] 
from #Real r 
left join #Backup b on r.realID = b.realid 
order by r.[RealID] 

Answer 2

对于任何预2012 ....

（*现在编辑假设所有realIDs将在真正的表存在）

SELECT   
    firstB.minBU AS [first Backup] 
    , R.realid 
    , ISNULL(B.numeric, R.numeric) AS [original value] 
FROM    
    (SELECT realid, MIN(backupid) AS minBU 
     FROM test.[backup] AS backup_1 GROUP BY realid 
    ) AS firstB 
    INNER JOIN 
    test.[backup] AS B 
     ON firstB.realid = B.realid AND firstB.minBU = B.backupid 
    RIGHT OUTER JOIN 
     test.real AS R ON firstB.realid = R.realid 

Answer 3

我发现这个职位上的SO：

Select from table if record found in another table

的回答这个问题帮我弥补了这样一个解决方案：

SELECT NULL AS BackupId, A.* FROM real-table A 
WHERE NOT EXISTS (
    SELECT * 
    FROM backup-table B 
    WHERE B.RealId = A.RealId 
) 

union all 

Select C.* FROM backup-table C 
INNER JOIN (
    SELECT MIN(BackupId) AS BackupId, 
      RealId 
     FROM backup-table 
     GROUP BY RealId 
    ) D 
on D.BackupId = C.BackupId 

ORDER BY RealId Asc 

不过，我想测试这一对cloudsafes回答，看它有更好的表现。