Re: SQL-spec incompatibilities in similar_escape() and related stuff

I wrote:
> I propose therefore that we leave similar_escape in place with its
> current behavior, as a compatibility measure for cases like this.
> Intead, invent two new strict functions, say
> 	similar_to_escape(pattern)
> 	similar_to_escape(pattern, escape)
> and change the parser and the implementation of SUBSTRING() to
> rely on these going forward.

> The net effect will be to make explicit "ESCAPE NULL" spec-compliant,
> and to get rid of the performance problem from inlining failure for
> substring().  All else is just doc clarifications.

Here's a proposed patch for that.  I think it's a bit too late to be
messing with this kind of thing for v12, so I'll add this to the
upcoming CF.

			regards, tom lane