题解 | #用where过滤空值练习#
用where过滤空值练习
http://www.nowcoder.com/practice/08c9846a423540319eea4be44e339e35
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
