Comment puis-je transformer une relation un-à-plusieurs dans Informix SQL en une seule ligne avec des valeurs séparées par des virgules ?

id     codes
63592  PELL
58640  SUBL
58640  USBL
73571  PELL
73571  USBL
73571  SUBL

id     codes 
63592  PELL
58640  SUBL, USBL
73571  PELL, USBL, SUBL

CREATE AGGREGATE group_concat
    WITH (INIT = gc_init, ITER = gc_iter,
          COMBINE = gc_comb, FINAL = gc_fini);

CREATE FUNCTION gc_init(dummy VARCHAR(255)) RETURNING LVARCHAR;
    RETURN '';
END FUNCTION;

CREATE FUNCTION gc_iter(result LVARCHAR, value VARCHAR(255))
    RETURNING LVARCHAR;
    IF result = '' THEN
        RETURN TRIM(value);
    ELSE
        RETURN result || ',' || TRIM(value);
    END IF;
END FUNCTION;

CREATE FUNCTION gc_comb(partial1 LVARCHAR, partial2 LVARCHAR)
    RETURNING LVARCHAR;
    IF partial1 IS NULL OR partial1 = '' THEN
        RETURN partial2;
    ELIF partial2 IS NULL OR partial2 = '' THEN
        RETURN partial1;
    ELSE
        RETURN partial1 || ',' || partial2;
    END IF;
END FUNCTION;

CREATE FUNCTION gc_fini(final LVARCHAR) RETURNING LVARCHAR;
    RETURN final;
END FUNCTION;

SELECT id, group_concat(codes)
    FROM anonymous_table
    GROUP BY id;