From: | Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | vadim(at)krs(dot)ru (Vadim Mikheev) |
Cc: | bamby(at)marka(dot)net(dot)ua, hackers(at)postgreSQL(dot)org |
Subject: | Re: [HACKERS] Re: [BUGS] General Bug Report: Bug in optimizer |
Date: | 1999-03-18 20:13:23 |
Message-ID: | 199903182013.PAA07350@candle.pha.pa.us |
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Thread: | |
Lists: | pgsql-bugs pgsql-hackers |
> Agreed, this is ok as long as
>
> vac=> create table table1 (field1 int);
> CREATE
> vac=> insert into table1 values (1);
> INSERT 1583349 1
> vac=> create index i_table1__field1 on table1 (field1);
> CREATE
> vac=> explain select * from table1 where field1 = 1;
> NOTICE: QUERY PLAN:
>
> Seq Scan on table1 (cost=1.03 size=1 width=4)
>
> - SeqScan is used for small tables.
>
> So, only bug reported is left.
I see it now. The -4 is coming over as a unary minus, and a 4. That is
OK, because the executor knows how to deal with a unary minus, but the
optimizer thinks it is a operator and a constant, which it is, but it
does not know how to index an operator with a constant.
Unary minus is probably the not only operator that can be auto-folded
into the constant. In fact, it may be valuable to auto-fold all
operator-constant pairs into just constants.
In fact, that may not be necessary. If we code so that we check that
the right-hand side is totally constants, and make the change in the
executor(if needed), we can just pass it all through. However, we need
the constant for optimizer min/max comparisons when using >, but we
could do without that if needed, so we don't have to evaluate operators
and functions outside the executor.
The quick fix may be to just make sure -4 does not use unary minus in
the parser.
--
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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