Question

My question is quite similar to Restricting a LEFT JOIN, with a variation.

Assuming I have a table SHOP and another table LOCATION. Location is a sort of child table of table SHOP, that has two columns of interest, one is a Division Key (calling it just KEY) and a “SHOP” number. This matches to the Number “NO” in table SHOP.

I tried this left outer join:

SELECT S.NO, L.KEY
FROM SHOP S
LEFT OUTER JOIN LOCATN L ON S.NO = L.SHOP

but I’m getting a lot of duplicates since there are many locations that belong to a single shop. I want to eliminate them and just get a list of “shop, key” entries without duplicates.

The data is correct but duplicates appear as follows:

SHOP     KEY
 1       XXX
 1       XXX
 2       YYY
 3       ZZZ
 3       ZZZ  etc.

I would like the data to appear like this instead:

SHOP     KEY
 1       XXX
 2       YYY
 3       ZZZ  etc.

SHOP table:

 NO
 1       
 2       
 3       

LOCATION table:

 LOCATION   SHOP  KEY
   L-1       1    XXX   
   L-2       1    XXX   
   L-3       2    YYY   
   L-4       3    YYY   
   L-5       3    YYY   

(ORACLE 10g Database)

Answer 1

You need to GROUP BY ‘S.No’ & ‘L.KEY’

SELECT S.NO, L.KEY 
FROM SHOP S 
LEFT OUTER JOIN LOCATN L 
ON S.NO = L.SHOP
GROUP BY S.NO, L.KEY