Re: like/ilike improvements

Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> Tom Lane wrote:
>> I thought we'd determined that advancing bytewise for "%" was also
>> risky, in two cases:
>>
>> 1. Multibyte character set that is not UTF8 (more specifically, does not
>> have a guarantee that first bytes and not-first bytes are distinct)

> I thought we disposed of the idea that there was a problem with charsets
> that didn't do first byte special.

We disposed of that in connection with a version of the patch that had
"%" advancing in NextChar units, so that comparison of ordinary
characters was always safely char-aligned. Consider 2-byte characters
represented as {AB} etc:

DATA x{AB}{CD}y

PATTERN %{BC}%

If "%" advances by bytes then this will find a spurious match. The
only thing that prevents it is if "B" can't be both a leading and a
trailing byte of validly-encoded MB characters.

regards, tom lane