Re: Need a query to get the difference of two tables

[Roger Baklund]

Michael Stassen wrote:
Roger Baklund wrote:
[...]
select a.address
  from a
  left join b on b.iid=a.id
  where b.iid is null;

That's not equivalent, because it leaves out a condition.  I think it 
should be

  SELECT a.address
  FROM a
  LEFT JOIN b ON a.id = b.iid AND b.message='y'
  WHERE b.iid IS NULL;
You are of course right, thank you! :)
...and the important thing here is to put this extra condition in the ON 
clause, not in the WHERE clause.

--
Roger
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