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Re: [SQL] More efficient DELETE ... ?

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: The Hermit Hacker <scrappy(at)hub(dot)org>, pgsql-sql(at)postgresql(dot)org
Subject: Re: [SQL] More efficient DELETE ... ?
Date: 2000-01-22 19:37:39
Message-ID: 200001221937.OAA25487@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-sql
> The Hermit Hacker <scrappy(at)hub(dot)org> writes:
> > This looks painful ...
> 
> > DELETE FROM webhit_referer_raw
> >       WHERE oid IN ( SELECT w.oid
> >                        FROM webhit_referer_raw w, referrer_data r
> >                       WHERE stat_date < 'Jan 17 2000 15:05:00'
> >                         AND w.referrer_url = r.referrer );
> 
> I believe you can do
> 
> DELETE FROM webhit_referer_raw
> WHERE referrer_url = referrer_data.referrer
>       AND referrer_data.stat_date < 'Jan 17 2000 15:05:00';
> 
> (I assume stat_date is in referrer_data, otherwise this'd be easy.)
> 
> This is an example where Postgres' willingness to create implicit FROM
> clause entries is a win ... AFAIK you couldn't do it in standard SQL,
> since for some reason DELETE doesn't take a FROM clause.

Good point.  I had forgotten all about that.

Should I cover that in my book?

What about the NOTICE we were going to add when this happens.  You will
see a WARN_FROM define in parser/*.c.  I had to disable the message
because the regression tests were failing.  They have to be regenerated
after I do this, but I can't do that here.  Do people still want the
message?  Can someone regenerate the regression output after I am done?

In fact, someone can just remove the #ifdef WARN_FROM defines around the
code and regenerate the regression tests and all will stay in sync.


-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  pgman(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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