Thread

1. RE: [GENERAL] IN/NOT IN operators

   Jackson, DeJuan <djackson@cpsgroup.com> — 1998-10-01T16:59:31Z

   This may not be the answer you want to hear but you could just
   restructure it into an and-or query.
   select * from aa where (bb = 2 and ff = 3) or (bb = 4 and ff = 5);
   	-DEJ
   	
   
   > -----Original Message-----
   > From:	Sergei Chernev [SMTP:ser@nsu.ru]
   > Sent:	Wednesday, September 30, 1998 4:15 AM
   > To:	pgsql-general@hub.org
   > Subject:	[GENERAL] IN/NOT IN operators
   > 
   > Hello,
   > I want to ask you if there are the way to do:
   > select * from aa where (bb, ff) IN ((2,3),(4,5));
   > ERROR:  parser: parse error at or near "2"    :((
   > 
   > I see that it works with subselect:
   > select * from aa where (bb, ff) IN (select (bb,ff) from zz);
   > 
   > 
   > Thank you,
   > ---------------------------
   > Sergei Chernev
   > Internet: ser@nsu.ru
   > Phone: +7-3832-397354
   > 
   
   

2. CNF vs DNF

   Taral <taral@mail.utexas.edu> — 1998-10-01T17:55:39Z

   > select * from aa where (bb = 2 and ff = 3) or (bb = 4 and ff = 5);
   
   I've been told that the system restructures these in CNF (conjunctive normal
   form)... i.e. the above query turns into:
   
   select * from aa where (bb = 2 or bb = 4) and (ff = 3 or bb = 4) and (bb = 2
   or ff = 5) and (ff = 3 or ff = 5);
   
   Much longer and much less efficient, AFAICT. Isn't it more efficient to do a
   union of many queries (DNF) than an intersection of many subqueries (CNF)?
   Certainly remembering the subqueries takes less memory... Also, queries
   already in DNF are probably more common than queries in CNF, requiring less
   rewrite.
   
   Can someone clarify this?
   
   Taral