Add current substring regular expression syntax
SQL:1999 had syntax
SUBSTRING(text FROM pattern FOR escapechar)
but this was replaced in SQL:2003 by the more clear
SUBSTRING(text SIMILAR pattern ESCAPE escapechar)
but this was never implemented in PostgreSQL. This patch adds that
new syntax as an alternative in the parser, and updates documentation
and tests to indicate that this is the preferred alternative now.
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Reviewed-by: Fabien COELHO <coelho@cri.ensmp.fr>
Discussion: https://www.postgresql.org/message-id/flat/
a15db31c-d0f8-8ce0-9039-
578a31758adb%402ndquadrant.com