From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com> |
Cc: | Joe Conway <mail(at)joeconway(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: bug in substring??? |
Date: | 2004-02-07 06:39:13 |
Message-ID: | 17305.1076135953@sss.pgh.pa.us |
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"scott.marlowe" <scott(dot)marlowe(at)ihs(dot)com> writes:
> thanks. I just got done looking up the SQL explanation, and I think my
> head exploded. Thanks for the heads up.
The formal definition seems unnecessarily complicated :-(, but the spec
authors' intent is reasonably clear from this paragraph in the
"Concepts" section of SQL92:
<character substring function> is a triadic function, SUBSTRING,
that returns a string extracted from a given string according
to a given numeric starting position and a given numeric length.
Truncation occurs when the implied starting and ending positions
are not both within the given string.
In other words, they consider that a zero or negative start position
should be truncated back to the actual start position (1) in much the
same way that a too-large length specification would be truncated to
match the actual end position.
AFAICT the only case in which SUBSTRING is supposed to raise an error is
when you specify a negative length.
regards, tom lane
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