Informix SQL の 1 対多の関係をカンマ区切りの値を含む単一の行に変換するにはどうすればよいですか?

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;