Re: [PATCH] proposal for regexp_count, regexp_instr, regexp_substr and regexp_replace

Hi,

This is a new version of the patch that now implements all the XQUERY
regexp functions as described in the standard, minus the differences of
PostgerSQL regular expression explain in [1].

The standard SQL describe functions like_regex(), occurrences_regex(),
position_regex(), substring_regex() and translate_regex() which
correspond to the commonly named functions regexp_like(),
regexp_count(), regexp_instr(), regexp_substr() and regexp_replace() as
reported by Chapman Flack in [2]. All these function are implemented in
the patch. Syntax of the functions are:

- regexp_like(string, pattern [, flags ])

- regexp_count( string, pattern [, position ] [, flags ])

- regexp_instr( string, pattern [, position ] [, occurrence ] [,
returnopt ] [, flags ] [, group ])

- regexp_substr( string, pattern [, position ] [, occurrence ] [, flags
] [, group ])

- regexp_replace(source, pattern, replacement [, position ] [,
occurrence ] [, flags ])

In addition to previous patch version I have added the regexp()_like
function and extended the existsing regex_replace() function. The patch
documents these functions and adds regression tests for all functions. I
will add it to the commitfest.

An other regexp functions regexp_positions() that returns all
occurrences that matched a POSIX regular expression is also developped
by Joel Jacobson, see [2]. This function expands the list of regexp
functions described in XQUERY.

[1]
https://www.postgresql.org/docs/13/functions-matching.html#FUNCTIONS-POSIX-REGEXP

[2]
https://www.postgresql.org/message-id/flat/bf2222d5-909d-408b-8531-95b32f18d4ab%40www.fastmail.com#3ec8ba658eeabcae2ac6ccca33bd1aed

--
Gilles Darold
LzLabs GmbH
http://www.lzlabs.com/