null範囲を含むMySQLGROUPBY年齢範囲

範囲テーブル（私の好みがあります）の代わりに、単一行の答えは次のようになります：

SELECT
    SUM(IF(age < 20,1,0)) as 'Under 20',
    SUM(IF(age BETWEEN 20 and 29,1,0)) as '20 - 29',
    SUM(IF(age BETWEEN 30 and 39,1,0)) as '30 - 39',
    SUM(IF(age BETWEEN 40 and 49,1,0)) as '40 - 49',
...etc.
FROM inquiries;