1:查询user_id等于1 的数据
Select * from user where user_id = 1
2:查询user_age大于等于12的数据
Select * from user where user_age >=12
3:查询user_age不等于12的数据
Select * from user where user_age <> 12
Select * from user where user_id = 1
Select * from user where user_age >=12
Select * from user where user_age <> 12