MySQLでUnionと組み合わせたRand関数の使用方法

from句が次のような一時テーブルのような外部SQLを作成できます。

 SELECT food_name from (
  SELECT foodName
  FROM food
  WHERE foodCategory_id = 1 OR 2
  ORDER BY RAND() limit 1) a
 UNION
 SELECT food_name from (
  SELECT foodName
  FROM food
  WHERE foodCategory_id = 7 OR 8 OR 9
  ORDER BY RAND() limit 1) b
 UNION
 SELECT food_name from (
  SELECT foodName
  FROM food
  WHERE foodCategory_id = 10 OR 11
  ORDER BY RAND() limit 1) c