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

Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> writes:
> "Andrew" == Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> writes:
> Andrew> The ESCAPE part could in theory be ambiguous if the SIMILAR
> Andrew> expression ends in a ... SIMILAR TO xxx operator, since then we
> Andrew> wouldn't know whether to attach the ESCAPE to that or keep it
> Andrew> as part of the function syntax. But I think this is probably a
> Andrew> non-issue. More significant is that ... COLNAME ! ESCAPE ...
> Andrew> again has postfix- vs. infix-operator ambiguities.

> And this ambiguity shows up already in other contexts:

> select 'foo' similar to 'f' || escape escape escape from (values ('oo')) v(escape);
> psql: ERROR: syntax error at or near "escape"
> LINE 1: select 'foo' similar to 'f' || escape escape escape from (va...

Hmm. Oddly, you can't fix it by adding parens:

regression=# select 'foo' similar to ('f' || escape) escape escape from (values ('oo')) v(escape);
psql: ERROR: syntax error at or near "escape"
LINE 1: select 'foo' similar to ('f' || escape) escape escape from (...
^

Since "escape" is an unreserved word, I'd have expected that to work.
Odd.

The big picture here is that fixing grammar ambiguities by adding
precedence is a dangerous business :-(

regards, tom lane