Re: Question on OUTER JOINS.

--- Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Ludwig Lim <lud_nowhere_man@yahoo.com> writes:
> >   1) Is the ON clause of an OUTER JOIN always
> > evaluated first before the WHERE clause?
> 
> No; the planner will do whatever it thinks is the
> most efficient way
> (assuming it can prove that the reordering it wants
> to do won't change
> the query result).
 If re-ordering does change the result, is the ON
clause evaluated first and the WHERE filters out the
result of the OUTER JOIN?


> >   Is there a way to rewrite the query as a view
> such
> > that one can do:
> 
> I'm really not clear on what you want here.  Better
> example please?
>   Sorry for not making it that clear.
  Is there way of rewritting :  SELECT  a.status,          employee_id  FROM   permission a LEFT JOIN          ( SELECT
*FROM employee WHERE employee_id
 
=5) as b ON (a.status = b.status)  WHERE status='test'

into a query that has no subselect in the FROM clause.I mean can the query above be rewritten into
something like:   SELECT a.status,         b.employee_id  FROM permission a LEFT JOIN employee b ON       (a.status =
b.status) WHERE a.status = 'test' and         b.employee_id = 5;
 

Thank you very much,

ludwig
  

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