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From:Dan Nelson Date:June 8 2000 6:36pm
Subject:Re: AND NOT ( X AND Y ) != AND ( !X OR !Y ) ?
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In the last episode (Jun 08), Sander Pilon said:
> Yes, they can be null. In fact, the table is a the result of a left
> join between two tables, and only '1' values are present for the
> flags.
> 
> I see the problem now. Is this standard SQL behaviour? Because
> boolean logic seems lost, in the way that you can rewrite a logical
> expression into a equivalent expression but get different results.

SQL logic isn't boolean, though.  It's tristate.  TRUE, FALSE, and
NULL.  Any comparison with NULL returns NULL, except for IS NULL (which
returns true) and IS NOT NULL (which returns false).

-- 
	Dan Nelson
	dnelson@stripped
Thread
Running mysql on windows 2000Basil Honikman8 Jun
  • AND NOT ( X AND Y ) != AND ( !X OR !Y ) ?Sander Pilon8 Jun
    • Re: AND NOT ( X AND Y ) != AND ( !X OR !Y ) ?Jeremy Cole8 Jun
      • Re: AND NOT ( X AND Y ) != AND ( !X OR !Y ) ?Jeremy Cole8 Jun
    • Re: AND NOT ( X AND Y ) != AND ( !X OR !Y ) ?Dan Nelson8 Jun
      • RE: AND NOT ( X AND Y ) != AND ( !X OR !Y ) ?Sander Pilon8 Jun
        • Re: AND NOT ( X AND Y ) != AND ( !X OR !Y ) ?Dan Nelson8 Jun
  • Re: Running mysql on windows 2000Carsten Gehling9 Jun
RE: AND NOT ( X AND Y ) != AND ( !X OR !Y ) ?Sander Pilon8 Jun