Question

I’m trying to fix an issue with a legacy database. The quote_literal function is not working for a specific database on an 8.4 install of postgres.

Here’s my results on a fresh test database:

select quote_literal(42);
 quote_literal 
---------------
 '42'
(1 row)

And now the same on the target db

select quote_literal(42);
ERROR:  function quote_literal(integer) is not unique
LINE 1: select quote_literal(42);
           ^
HINT:  Could not choose a best candidate function. You might need to add explicit type casts.

AIUI, the quote_literal(anyvalue) function should handle integer values ok, and this seems to be upheld by the first test.

So I figured the quote_literal function must have been overridden in this db but no this doesn’t seem to be the case. I could override it with a specific quote_literal(integer) function but I don’t see why I should have to.

The question is what is could be causing the failure of this function in this specific database whilst not affecting the fresh db?

Answer 1

Another possibility: Somebody has added implicit casts from text to your database. This was a common workaround for an intentional BC break in 8.3. See the release notes for 8.3, E.57.2. Migration to Version 8.3

Demo:

regress=# \df quote_literal
                              List of functions
   Schema   |     Name      | Result data type | Argument data types |  Type  
------------+---------------+------------------+---------------------+--------
 pg_catalog | quote_literal | text             | anyelement          | normal
 pg_catalog | quote_literal | text             | text                | normal
(2 rows)
regress=# CREATE FUNCTION pg_catalog.text(integer) RETURNS text STRICT IMMUTABLE LANGUAGE SQL AS 'SELECT textin(int4out($1));';
CREATE FUNCTION
regress=# CREATE CAST (integer AS text) WITH FUNCTION pg_catalog.text(integer) AS IMPLICIT;
CREATE CAST
regress=# SELECT quote_literal(42);
ERROR:  function quote_literal(integer) is not unique
LINE 1: SELECT quote_literal(42);
               ^
HINT:  Could not choose a best candidate function. You might need to add explicit type casts.
regress=# 

This’ll fix it, but probably break other code that’s still relying on the cast:

regress=# DROP CAST (integer AS text);
DROP CAST
regress=# SELECT quote_literal(42);
 quote_literal 
---------------
 '42'
(1 row)