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limit to 1 row on the right side of left join

Posted on 2009-04-09
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Last Modified: 2012-05-06
My desired output is something like this, to show only one (any one) owner per project:
1      projectA        Joe             1
2      projectB        Sue             1
3      projectC        Mike            1
4      projectD        NULL      NULL
5      projectE        NULL      NULL

Considering data from the Left side of a join:
SELECT     ProjID, Descript FROM         tmpProjects
1      projectA  
2      projectB  
3      projectC  
4      projectD  
5      projectE  
NULL      NULL

And a table from the right side of the join:
SELECT     RecNo, ProjID, UserID, Owner FROM         tmpAssigned
100      1      Joe             1
101      2      Sue             1
102      2      John            0
103      3      Mike            1
104      3      Katy            1
105      3      Jennifer        NULL
106      4      NULL      0
 
The query below is very close :
SELECT     dbo.tmpProjects.ProjID, dbo.tmpProjects.Descript, dbo.tmpAssigned.UserID, dbo.tmpAssigned.Owner FROM         dbo.tmpProjects LEFT OUTER JOIN dbo.tmpAssigned ON dbo.tmpProjects.ProjID = dbo.tmpAssigned.ProjID AND dbo.tmpAssigned.Owner = 1

and results in this:                      
1      projectA        Joe             1
2      projecB         Sue             1
3      projectC        Mike            1
3      projectC        Katy            1
4      projectD        NULL      NULL
5      projectE        NULL      NULL

But it doesn't consider the fact that there could be more than one owner.  
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Question by:thefumbler
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6 Comments
 
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Expert Comment

by:ralmada
ID: 24112649
If it doesn't matter who's the owner.
SELECT     dbo.tmpProjects.ProjID, min(dbo.tmpProjects.Descript), min(dbo.tmpAssigned.UserID), dbo.tmpAssigned.Owner FROM         dbo.tmpProjects 
LEFT OUTER JOIN dbo.tmpAssigned ON dbo.tmpProjects.ProjID = dbo.tmpAssigned.ProjID AND dbo.tmpAssigned.Owner = 1
group by dbo.tmpProjects.ProjID

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Expert Comment

by:ralmada
ID: 24112652
sorry missed something
SELECT     dbo.tmpProjects.ProjID, min(dbo.tmpProjects.Descript), min(dbo.tmpAssigned.UserID), min(dbo.tmpAssigned.Owner) FROM         dbo.tmpProjects 
LEFT OUTER JOIN dbo.tmpAssigned ON dbo.tmpProjects.ProjID = dbo.tmpAssigned.ProjID AND dbo.tmpAssigned.Owner = 1
group by dbo.tmpProjects.ProjID

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Author Comment

by:thefumbler
ID: 24112680
thanks ralmada...technically that works, but I guess I didn't explain thoroughly.  I'm trying to add all of the right side of the LEFT OUTER JOIN join to a much larger more complicated query with a lot of joins without disturbing the existing query, at least as little as possible.  So I hope to avoid group by types of changes.  

Is there a way to do this without altering the left side with a group by syntax?

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LVL 41

Expert Comment

by:ralmada
ID: 24112694
You can try this:
SELECT     
	dbo.tmpProjects.ProjID, 
	dbo.tmpProjects.Descript, 
	a.UserID, 
	a.Owner 
FROM         dbo.tmpProjects 
LEFT OUTER JOIN (select ProjID, min(UserID), min(Owner) from dbo.tmpAssigned group by ProjID) a
ON dbo.tmpProjects.ProjID = a.ProjID AND a.Owner = 1

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Accepted Solution

by:
ralmada earned 250 total points
ID: 24112699
I mean
SELECT     
	dbo.tmpProjects.ProjID, 
	dbo.tmpProjects.Descript, 
	a.UserID, 
	a.Owner 
FROM         dbo.tmpProjects 
LEFT OUTER JOIN (select ProjID, min(UserID) as UserID, min(Owner) as Owner from dbo.tmpAssigned group by ProjID) a
ON dbo.tmpProjects.ProjID = a.ProjID AND a.Owner = 1

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Author Comment

by:thefumbler
ID: 24112708
yep, that's more what I was going towards.  thanks!
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