SQL daily exercise - niuke.com

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Catalog

The purpose of this article is ：

SQL1  Query all columns

Example 1

SQL2  Query multiple columns

Example 1

SQL3  Query result de duplication

Example 1

SQL4  Query results limit the number of rows returned

Example 1

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The following are all exercises of niuke.com -mysql Database test results ：

SQL1  Query all columns

subject ： Now the operator wants to view all the data in the user information table , Please take out the corresponding results

Example ：user_profile

id	device_id	gender	age	university	province
1	2138	male	21	Peking University,	Beijing
2	3214	male		Fudan University	Shanghai
3	6543	female	20	Peking University,	Beijing
4	2315	female	23	Zhejiang University	ZheJiang
5	5432	male	25	Shandong University	Shandong

According to the example , Your query should return the following results :

id	device_id	gender	age	university	province
1	2138	male	21	Peking University,	Beijing
2	3214	male		Fudan University	Shanghai
3	6543	female	20	Peking University,	Beijing
4	2315	female	23	Zhejiang University	Zhejiang
5	5432	male	25	Shandong University	Shandong

Example 1

Input ：

drop table if exists user_profile;
CREATE TABLE `user_profile` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`gender` varchar(14) NOT NULL,
`age` int ,
`university` varchar(32) NOT NULL,
`province` varchar(32)  NOT NULL);
INSERT INTO user_profile VALUES(1,2138,'male',21,' Peking University, ','BeiJing');
INSERT INTO user_profile VALUES(2,3214,'male',null,' Fudan University ','Shanghai');
INSERT INTO user_profile VALUES(3,6543,'female',20,' Peking University, ','BeiJing');
INSERT INTO user_profile VALUES(4,2315,'female',23,' Zhejiang University ','ZheJiang');
INSERT INTO user_profile VALUES(5,5432,'male',25,' Shandong University ','Shandong');

Copy output ：

1|2138|male|21| Peking University, |BeiJing
2|3214|male|None| Fudan University |Shanghai
3|6543|female|20| Peking University, |BeiJing
4|2315|female|23| Zhejiang University |ZheJiang
5|5432|male|25| Shandong University |Shandong

select * from user_profile;

 perhaps 

select 
  id,device_id,
  gender,
  age,
  university,province
from user_profile;

SQL2  Query multiple columns

subject ： Now, the students want to operate the user's equipment id The corresponding gender 、 Data on age and school , Please take out the corresponding data

Example ：user_profile

id	device_id	gender	age	university	province
1	2138	male	21	Peking University,	Beijing
2	3214	male		Fudan University	Shanghai
3	6543	female	20	Peking University,	Beijing
4	2315	female	23	Zhejiang University	Zhejiang
5	5432	male	25	Shandong University	Shandong

According to the example , Your query should return the following results

device_id	gender	age	university
2138	male	21	Peking University,
3214	male		Fudan University
6543	female	20	Peking University,
2315	female	23	Zhejiang University
5432	male	25	Shandong University

Example 1

Input ：

drop table if exists user_profile;
CREATE TABLE `user_profile` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`gender` varchar(14) NOT NULL,
`age` int ,
`university` varchar(32) NOT NULL,
`province` varchar(32)  NOT NULL);
INSERT INTO user_profile VALUES(1,2138,'male',21,' Peking University, ','BeiJing');
INSERT INTO user_profile VALUES(2,3214,'male',null,' Fudan University ','Shanghai');
INSERT INTO user_profile VALUES(3,6543,'female',20,' Peking University, ','BeiJing');
INSERT INTO user_profile VALUES(4,2315,'female',23,' Zhejiang University ','ZheJiang');
INSERT INTO user_profile VALUES(5,5432,'male',25,' Shandong University ','Shandong');

Copy output ：

2138|male|21| Peking University, 
3214|male|None| Fudan University 
6543|female|20| Peking University, 
2315|female|23| Zhejiang University 
5432|male|25| Shandong University 

select device_id,gender,age,university 
from user_profile;

SQL3  Query result de duplication

subject ： Now the operation needs to check which schools users come from , Please take the school's de duplication data from the user information table .

Example :user_profile

id	device_id	gender	age	university	province
1	2138	male	21	Peking University,	Beijing
2	3214	male		Fudan University	Shanghai
3	6543	female	20	Peking University,	Beijing
4	2315	female	23	Zhejiang University	ZheJiang
5	5432	male	25	Shandong University	Shandong

According to the example , Your query should return the following results ：

university

Peking University,

Fudan University

Zhejiang University

Shandong University

Example 1

Input ：

drop table if exists user_profile;
CREATE TABLE `user_profile` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`gender` varchar(14) NOT NULL,
`age` int ,
`university` varchar(32) NOT NULL,
`province` varchar(32)  NOT NULL);
INSERT INTO user_profile VALUES(1,2138,'male',21,' Peking University, ','BeiJing');
INSERT INTO user_profile VALUES(2,3214,'male',null,' Fudan University ','Shanghai');
INSERT INTO user_profile VALUES(3,6543,'female',20,' Peking University, ','BeiJing');
INSERT INTO user_profile VALUES(4,2315,'female',23,' Zhejiang University ','ZheJiang');
INSERT INTO user_profile VALUES(5,5432,'male',25,' Shandong University ','Shandong');

Copy output ：

 Peking University, 
 Fudan University 
 Zhejiang University 
 Shandong University 

select distinct university
from user_profile;
 perhaps 
SELECT university 
from user_profile 
GROUP BY university;

SQL4  Query results limit the number of rows returned

subject ： Now the operation only needs to check the front 2 User details equipment ID data , Please read the user information form  user_profile Take out the corresponding results .

Example ：

id	device_id	gender	age	university	province
1	2138	male	21	Peking University,	Beijing
2	3214	male		Fudan University	Shanghai
3	6543	female	20	Peking University,	Beijing
4	2315	female	23	Zhejiang University	ZheJiang
5	5432	male	25	Shandong University	Shandong

According to input , Your query should return the following results ：

device_id

2138

3214

Example 1

Input ：

drop table if exists user_profile;
CREATE TABLE `user_profile` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`gender` varchar(14) NOT NULL,
`age` int ,
`university` varchar(32) NOT NULL,
`province` varchar(32)  NOT NULL);
INSERT INTO user_profile VALUES(1,2138,'male',21,' Peking University, ','BeiJing');
INSERT INTO user_profile VALUES(2,3214,'male',null,' Fudan University ','Shanghai');
INSERT INTO user_profile VALUES(3,6543,'female',20,' Peking University, ','BeiJing');
INSERT INTO user_profile VALUES(4,2315,'female',23,' Zhejiang University ','ZheJiang');
INSERT INTO user_profile VALUES(5,5432,'male',25,' Shandong University ','Shandong');

Copy output ：

2138
3214

select device_id from user_profile limit 2;
select device_id from user_profile limit 0,2;
select device_id from user_profile limit 2 offset 0;
select device_id from user_profile where id in(1,2);
select device_id from user_profile where id <=2;
select device_id from user_profile where id=1 or id=2;