用最小日期更新临时表

Question

I'm trying to update the InsertDate for all the distinct AccId and AccNameHolder combinations in the #tmpResults table only if an earlier insert date exists.

The table schemas are like so:

#tmpResults

Trans | AccId | AccountNameHolder | EarlyDate | CardType 

PositionCollection

Id | AccId | InsertDate | BtchId

CardErrors

AccId | AccNameHolder | BtchId | TransId

Here is what I have tried so far:

UPDATE  RES  
SET     EarlyDate = pc.InsertDate   
FROM  ( dbo.PositionCollection pc    
        LEFT JOIN dbo.CardErrors ce ON ce.BtchId = pc.BtchId AND pc.id =     ce.Transid  )    
    INNER JOIN #tmpResults RES   
ON      RES.AccId = pc.AccId    
AND     RES.AccNameHolder = ce.AccNameHolder    
WHERE   RES.EarlyDate = (SELECT MIN(InsertDate) FROM PostionCollection)    
AND     RES.AccId = pc.AccId    
AND     RES.AccNameHolder = ce.AccNameHolder

Answer 1

Heres a few more general solutions, for where InsertDate is null, You can use them with DateDiff to change the conditions to earlier, later or whatever or just something like

OldInstDate <= COALESCE(NewInstDate, OldInstDate)

The conditional update can be achieved within the select statement so...

SET InsertDate = COALESCE(InsertDate, NewInsertDate) WHERE...

OR

SET InsertDate = CASE WHEN InsertDate IS NULL THEN NewInsertDate 
                      ELSE InsertDate END

OR

WHERE ...
AND InsertDate IS NULL

For really clear help on sub queries http://allenbrowne.com/subquery-01.html I think this is probably the best I've seen and http://allenbrowne.com/subquery-02.html for trouble shooting

Answer 2

Use derived table in your UPDATE statement

UPDATE x
SET x.EarlyDate = x.InsertDate  
FROM  ( 
       SELECT RES.EarlyDate, pc.InsertDate
       FROM dbo.PositionCollection pc
         LEFT JOIN dbo.CardErrors ce ON ce.BtchId = pc.BtchId AND pc.id = ce.Transid
         INNER JOIN #tmpResults RES ON RES.AccId = pc.AccId
           AND RES.AccNameHolder = ce.AccNameHolder
       WHERE RES.EarlyDate = (SELECT MIN(InsertDate) FROM PostionCollection) AND RES.AccId = pc.AccId
         AND RES.AccNameHolder = ce.AccNameHolder
       ) x

UPDATE 27.11.2012

UPDATE x
SET x.EarlyDate = x.InsertDate
FROM  (
       SELECT RES.EarlyDate, m.InsertDate
       FROM dbo.PositionCollection pc
         LEFT JOIN dbo.CardErrors ce ON ce.BtchId = pc.BtchId AND pc.id = ce.Transid
         INNER JOIN #tmpResults RES ON RES.AccId = pc.AccId AND RES.AccNameHolder = ce.AccNameHolder
         INNER JOIN (SELECT MIN(InsertDate) AS InsertDate FROM PostionCollection) m
           ON RES.EarlyDate = m.InsertDate 
       ) x