方法1:select device_id,gender,age,university from user_profile where age is not NULL --运行效率高
方法2:select device_id,gender,age,university from user_profile where age !='' --运行效率低
方法1:select device_id,gender,age,university from user_profile where age is not NULL --运行效率高
方法2:select device_id,gender,age,university from user_profile where age !='' --运行效率低