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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