Select the first row in a join of two tables in one statement

Question

I need to select only the first row from a query that joins tables A and B. On table B exist multiple records with same name. There are not identifiers in any of the two tab

Answer 1

Using a GROUP BY may get you part way there, but beware. If you do something like this:

Select A.NAME, min(B.DATA1), min(B.DATA2) 
From A Inner Join B on A.NAME = B.NAME 
Group by A.NAME;

You will get the result you are looking for:

  NAME      DATA1   DATA2
  sameName   1        2    
  otherName  5        7

But only because of the data you are testing with. If you change the data, so that instead of:

otherName  8        9

you had:

otherName  8        4

It would return:

  NAME      DATA1   DATA2
  sameName   1        2    
  otherName  5        4

Note that otherName does not return DATA1 and DATA2 from the same record!

Update: A self-join with a comparison on one of the data values may help you, such as:

SELECT a.*, b.* FROM a,b 
   LEFT JOIN b b2 ON b.name = b2.name AND b.data2 < b2.data2 
   WHERE a.name = b.name AND b2.data2 IS NOT NULL;

However, this will only work if the values in DATA2 are unique per NAME.