练习直通门

非技术快速入门

1. 查询多列 select 字段名 from 表名

select device_id, gender, age, university from user_profile;

2. 查询所有列

SELECT id, device_id, gender, age, university, province FROM user_profile;

3. 查询结果去重 相关博客
   使用distinct关键字去重：在需要去重的字段前加distinct

select distinct university FROM user_profile;

4. 查询结果限制返回行数

• where用于添加限制条件

  SELECT device_id FROM user_profile WHERE id<=2; 	
  

• limit 添加限制条件

  SELECT device_id FROM user_profile limit 0, 2;
  

5. 将查询后的列重新命名

   SELECT device_id as user_infos_example from user_profile limit 0,2;
   

   as可以省略

   SELECT device_id  user_infos_example from user_profile limit 0,2;
   

6. 查找学校是北大的学生信息

SELECT device_id, university from user_profile where university='北京大学';

7. 查找年龄大于24岁的用户信息

SELECT device_id, gender, age, university FROM user_profile where age>24;

8. 查找某个年龄段的用户信息

• 利用and

select device_id, gender, age from user_profile WHERE age>=20 and age <= 23;

• 利用between

select device_id, gender, age from user_profile where age BETWEEN 20 and 23;

9. 查找除复旦大学的用户信息

• where

SELECT device_id, gender, age, university FROM user_profile where university != '复旦大学';

• not in

SELECT device_id,gender,age,university FROM user_profile WHERE university NOT IN ('复旦大学');

10. 用where过滤空值练习

SELECT device_id, gender, age, university from user_profile 
WHERE age!='';

SELECT device_id, gender, age, university from user_profile 
WHERE age is not NULL;