SIMILAR TO incorrect with alternation

Hello,

We just had a case where invalid data entered our database, causing
application failure. A constraint was in place to prevent this and
appeared correct, however, I was able to verify that the expression was
evaluating to TRUE when I expected it to be FALSE. As a work around we
have fallen back to the nonstandard POSIX regular expression support,
which works correctly.

Here is a simple test case which triggers the problematic behavior. I
would expect the SQL regular expression and POSIX regular expression
below to give the same results. However, they produce different
answers. The difference seems to be caused by a naive implementation of
similar_escape(text, text) as also demonstrated below.

unidb=# select version();

version
-----------------------------------------------------------------------------------------------------------
PostgreSQL 8.1.3 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.3.5
20050117 (prerelease) (SUSE Linux)
(1 row)

unidb=# select 'ab' similar to 'a|b';
?column?
----------
t
(1 row)

unidb=# select 'ab' ~ '^(a|b)$';
?column?
----------
f
(1 row)

unidb=# select similar_escape('a|b', NULL);
similar_escape
----------------
^a|b$
(1 row)

Thanks,

--
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Aaron Bingham
Senior Software Engineer
Cenix BioScience GmbH
Tatzberg 47 phone: +49 (351) 4173-146
D-01307 Dresden, Germany fax: +49 (351) 4173-198
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