题解 | #截取出年龄#

select
  substring_index(substring_index(profile, ',',3), ',', -1) as age,
  //先截取出（a,b,c),再截取出 c
  count(device_id) as number
from
  user_submit
group by
  age
//注意很多次写对了但不通过都是因为用了中文的括号