テーブルの比較で、カラムの値を結合して比較 ref: http://qiita.com/xxxkurosukexxx/items/d760de028b609a0c1646

file0.sql

SELECT
  *
FROM
  table_a
  LEFT OUTER JOIN
    table_b
  ON
    (a_item_id = b_item_no and a_code = concat(b_x, b_y, b_z))
WHERE
  b.item_no IS NULL;

file1.sql

SELECT
  *
FROM
  table_a
WHERE
  NOT EXISTS (
    SELECT
      NULL
    FROM
      table_b
    WHERE
      a_item_id = b_item_no
      and a_code = concat(b_x, b_y, b_z)
  )
;