Обсуждение: BUG #2729: Backslash escaping not working as expected

The following bug has been logged online:

Bug reference:      2729
Logged by:          Michael van Rooyen
Email address:      mvanr@bigfoot.com
PostgreSQL version: 8.1.4
Operating system:   Linux
Description:        Backslash escaping not working as expected
Details:

The following query from psql:

select * from product where name like '%\\%';

Yields products whose names end with a %. I would have expected it to yeild
products whose names contained a backslash.

"Michael van Rooyen" <mvanr@bigfoot.com> writes:
> The following query from psql:
> select * from product where name like '%\\%';
> Yields products whose names end with a %. I would have expected it to yeild
> products whose names contained a backslash.

Postgres defaults to assuming \ as the LIKE escape character, that is,
what you typed is equivalent to

select * from product where name like '%\\%' escape '\\';

You can get the behavior you're expecting by not having any escape character:

select * from product where name like '%\\%' escape '';

This is as explained in TFM:
http://www.postgresql.org/docs/8.1/static/functions-matching.html#FUNCTIONS-LIKE
although I notice that SQL92 says that there is no escape character by
default.  We can't change our historical documented behavior on the
point unless we were willing to provide a configuration variable to
adjust it, and I'm not sure it's worth that.

            regards, tom lane