年龄段分组计数

    在统计人群特征数据时，需要将用户年龄分组来计数，mysql 里的  case when  可以直接实现的

SELECT
    age,
    count( * ) AS cnt 
FROM
    (
    SELECT
    CASE        
        WHEN info_t1 <= 20 THEN    '20' 
        WHEN info_t1 <= 30 AND info_t1 >= 21 THEN    '21-30' 
        WHEN info_t1 <= 40 AND info_t1 >= 31 THEN    '31-40' 
        WHEN info_t1 <= 50 AND info_t1 >= 41 THEN    '41-50' 
        WHEN info_t1 <= 60 AND info_t1 >= 51 THEN    '51-60' 
        WHEN info_t1 >= 61 THEN        '61' 
            END AS age 
        FROM
            `user_age` 
        ) AS a 
GROUP BY
    age