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Re: [HACKERS] SQL92

From: Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us>
To: djackson(at)cpsgroup(dot)com (Jackson, DeJuan)
Cc: lockhart(at)alumni(dot)caltech(dot)edu, pgsql-hackers(at)hub(dot)org
Subject: Re: [HACKERS] SQL92
Date: 1998-10-02 01:48:59
Message-ID: 199810020148.VAA22777@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
> > > Does the SQL92 standard have to be purchased from the ANSI Board?
> > 
> > afaik, yes.
> > 
> > > Well, my actual question has to do with LIKE.  Could anyone who has
> > a
> > > copy of a standard send me the PATTERN syntax/meanings for LIKE in
> > > SQL92?
> > 
> > Well, you may be hoping for more than is in any of your reference
> > books,
> > but there isn't any more to tell :)
> > 
> >   % ==> match any (sub)string
> >   _ ==> match any single character
> >   everything else matches itself
> > 
> > In SQL92 (but not yet in Postgres; can't remember if there is a
> > workaround):
> > 
> >   LIKE 'pattern' ESCAPE 'char'
> > 
> > allows a single character "char" if it precedes the two pattern
> > matching
> > characters to demote the "%" or "_" to act like a normal single
> > character. The Postgres regex stuff is much more powerful.
> > 
> > Sorry, I think that's it :(
> > 
> >                     - Tom
> Well, In all of the major Databases that I have worked with there is
> also the "[character_set]" matching operator.  
> So a pattern of '[A-D]%' would match all word beginning with "A", "B",
> "C", or "D", and "[^character_set]" matches everything but the set.
> Looking at the current PgSQL like code this is ignored as well as the
> ESCAPE syntax.  I'm trying to resolve the problem we have of LIKE not
> matching the pattern "%%" to anything even "%".
> But, looking at the code I see that "%%" or "%%%%%%%%" should be equal
> to "%" so it's not the LIKE matching code that's causing the problem
> (also, read I'm looking in the wrong spot).
> 
> Does anybody know if the "[character_set]" stuff is part of the
> standard?
> Can anyone point me to another place where the pattern could/would get
> munged?
> Also, wouldn't doing a memmove from the DATA portion of a varlena struct
> cause it problems if it was accessed again?
> 		Thanks again,

Added to TODO list:

	* have LIKE support character classes, 'pg_[a-c]%'

I did not realize we didn't have that.

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  maillist(at)candle(dot)pha(dot)pa(dot)us            |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026


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