Hola Mariu,
Para postgres 8.3 o superior tenes que ejecutar este script.
Abrí una conexión a la base y ejecutá esta consulta sql:
CREATE OR REPLACE FUNCTION pg_catalog.varchartoint(character varying) RETURNS integer
STRICT IMMUTABLE LANGUAGE SQL AS ‘SELECT
int4($1::text);’;
CREATE CAST (character varying AS integer) WITH FUNCTION pg_catalog.varchartoint(character varying) AS IMPLICIT;
Saludos,
Eugenia