Support '_' as escape char in LIKE

[TennyZhuang]

Currently, we banned _ as escape char in LIKE expression, since the output is not as expected.

The failed regress tests (commented):

--@ SELECT 'bear' LIKE 'b_ear' ESCAPE '_' AS "true";
--@ SELECT 'bear' NOT LIKE 'b_ear' ESCAPE '_' AS "false";

[github-actions]

This issue has been open for 60 days with no activity. Could you please update the status? Feel free to continue discussion or close as not planned.

[Max-Cheng]

@TennyZhuang new here. can i pick this?

[TennyZhuang]

@TennyZhuang new here. can i pick this?

Sure, thanks!

[Max-Cheng]

@TennyZhuang I got some weird behavior on this featrue deplyment #17377. Such as

SELECT '____' LIKE '_____' ESCAPE '_' as "true"

In PostgreSQL 16.3 will return

ERROR:  LIKE pattern must not end with escape character

But , in otherwise this query should be return true.

In other test case should return true but reutrn false

postgres=# SELECT '____r' LIKE '_____r' ESCAPE '_' as "true";
 true
------
 f
(1 row)

I throught this feature need more cornercase to verify.