Re: Prefix operator for text and spgist support

Hello,

On Fri, Feb 02, 2018 at 06:03:27PM +0300, Ildus Kurbangaliev wrote:
> Hi,
>
> Attached patch introduces prefix operator ^@ for text type. For 'a ^@ b'
> it returns true if 'a' starts with 'b'. Also there is spgist index
> support for this operator.
>
> It could be useful as an alternative for LIKE for 'something%'
> templates. Or even used in LIKE queries instead of ~>=~ and ~<~ in the
> future. But it would require new strategy for btree.

I've looked at the patch. It is applied and tests pass.

I have a couple comments:

> + if (ptype == Pattern_Type_Prefix)
> + {
> + char *s = TextDatumGetCString(constval);
> + prefix = string_to_const(s, vartype);
> + pstatus = Pattern_Prefix_Partial;
> + rest_selec = 1.0; /* all */
> + pfree(s);
> + }
> + else
> + pstatus = pattern_fixed_prefix(patt, ptype, collation,
> + &prefix, &rest_selec);

I think it is better to put Pattern_Type_Prefix processing into
pattern_fixed_prefix() as another case entry.

Secondly, it is worth to fix the documentation. At least here [1]. Maybe
there are another places where documentation should be fixed.

1 - https://www.postgresql.org/docs/current/static/spgist-builtin-opclasses.html

--
Arthur Zakirov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company