Миграция с PostgreSQL-9.2 на 9.0.1

CREATE OR REPLACE FUNCTION concat_func(text, text) RETURNS text AS '
    SELECT CASE WHEN $1 IS NULL OR $1 = \'\' THEN $2
            WHEN $2 IS NULL OR $2 = \'\' THEN $1
            ELSE $1 || $2
            END; 
'
 LANGUAGE SQL;

CREATE AGGREGATE concat (
  sfunc = concat_func,
  basetype = text,
  stype = text,
  initcond = ''
);