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Tutorial on the principle and application of database system (059) -- MySQL exercise questions: operation questions 1-10 (III)
2022-07-28 13:45:00 【Rsda DBA_ WGX】
Database system principle and Application Tutorial （059）—— MySQL Exercises ： Operation questions 1-10（ 3、 ... and ）
1、 Basic query （1）： Query all columns in the table
subject ： To view all the information in the user information table , To write SQL Statement to get the corresponding result .
Example ：user_profile The data in the table are as follows .
| 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 |
The 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 |
Table structure and data are as follows ：
/* 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'); */
answer ：
-- Use *
mysql> select * from user_profile;
+----+-----------+--------+------+--------------+----------+
| id | device_id | gender | age | university | province |
+----+-----------+--------+------+--------------+----------+
| 1 | 2138 | male | 21 | Peking University, | BeiJing |
| 2 | 3214 | male | NULL | Fudan University | Shanghai |
| 3 | 6543 | female | 20 | Peking University, | BeiJing |
| 4 | 2315 | female | 23 | Zhejiang University | ZheJiang |
| 5 | 5432 | male | 25 | Shandong University | Shandong |
+----+-----------+--------+------+--------------+----------+
5 rows in set (0.00 sec)
-- Use the field list
mysql> select id, device_id, gender, age, university, province from user_profile;
+----+-----------+--------+------+--------------+----------+
| id | device_id | gender | age | university | province |
+----+-----------+--------+------+--------------+----------+
| 1 | 2138 | male | 21 | Peking University, | BeiJing |
| 2 | 3214 | male | NULL | Fudan University | Shanghai |
| 3 | 6543 | female | 20 | Peking University, | BeiJing |
| 4 | 2315 | female | 23 | Zhejiang University | ZheJiang |
| 5 | 5432 | male | 25 | Shandong University | Shandong |
+----+-----------+--------+------+--------------+----------+
5 rows in set (0.00 sec)
2、 Basic query （2）： Query multiple columns
subject ： To query the user's device id The corresponding gender 、 Age and school information , Please take out the corresponding data , To write SQL Statement to get the corresponding result .
Example ：user_profile The data in the table are as follows .
| 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 |
The 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 |
answer ：
mysql> select device_id, gender, age, university from user_profile;
+-----------+--------+------+--------------+
| device_id | gender | age | university |
+-----------+--------+------+--------------+
| 2138 | male | 21 | Peking University, |
| 3214 | male | NULL | Fudan University |
| 6543 | female | 20 | Peking University, |
| 2315 | female | 23 | Zhejiang University |
| 5432 | male | 25 | Shandong University |
+-----------+--------+------+--------------+
5 rows in set (0.00 sec)
3、 Basic query （3）： Query result de duplication
subject ： To see which schools users come from , Get the school's de duplication data from the user information table .
Example ：user_profile The data in the table are as follows .
| 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 |
The query should return the following results ：
| university |
|---|
| Peking University, |
| Fudan University |
| Zhejiang University |
| Shandong University |
answer ：
mysql> select distinct university from user_profile;
+--------------+
| university |
+--------------+
| Peking University, |
| Fudan University |
| Zhejiang University |
| Shandong University |
+--------------+
4 rows in set (0.00 sec)
4、 Basic query （4）： Limit the number of rows returned from query results
subject ： Before you want to view 2 Devices of users ID data , From the user information table user_profile Take out the corresponding results .
Example ：user_profile The data in the table are as follows .
| 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 |
The query should return the following results ：
| device_id |
|---|
| 2138 |
| 3214 |
answer ：
mysql> select device_id from user_profile limit 2;
+-----------+
| device_id |
+-----------+
| 2138 |
| 3214 |
+-----------+
2 rows in set (0.00 sec)
5、 Basic query （5）： Specify an alias for the queried column
subject ： Before you want to view 2 Devices of users ID, And change the column name to ‘user_infos_example’, Take the corresponding results from the user information table .
Example ：user_profile The data in the table are as follows .
| 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 |
The query should return the following results ：
| user_infos_example |
|---|
| 2138 |
| 3214 |
answer ：
-- Don't use as
mysql> select device_id user_infos_example from user_profile limit 2;
+--------------------+
| user_infos_example |
+--------------------+
| 2138 |
| 3214 |
+--------------------+
2 rows in set (0.01 sec)
-- Use as
mysql> select device_id as user_infos_example from user_profile limit 2;
+--------------------+
| user_infos_example |
+--------------------+
| 2138 |
| 3214 |
+--------------------+
2 rows in set (0.00 sec)
6、 Comparison operator （1）： The inquiry school is 【 Peking University, 】 Student information
subject ： To screen out all the student information of Peking University , Take the data that meets the conditions from the user information table , Return device id And school .
Example ：user_profile The data in the table are as follows .
| 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 |
The query should return the following results ：
| device_id | university |
|---|---|
| 2138 | Peking University, |
| 6543 | Peking University, |
answer ：
mysql> select device_id, university from user_profile where university = ' Peking University, ';
+-----------+--------------+
| device_id | university |
+-----------+--------------+
| 2138 | Peking University, |
| 6543 | Peking University, |
+-----------+--------------+
2 rows in set (0.00 sec)
7、 Comparison operator （2）： Query age is greater than 24 Years old user information
subject ： To query 24 User information older than , Take out the equipment that meets the conditions ID、 Gender 、 Age 、 School .
User information sheet ：user_profile The data in the table are as follows .
| 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 |
The query should return the following results ：
| device_id | gender | age | university |
|---|---|---|---|
| 5432 | male | 25 | Shandong University |
answer ：
mysql> select device_id, gender, age, university from user_profile where age > 24;
+-----------+--------+------+--------------+
| device_id | gender | age | university |
+-----------+--------+------+--------------+
| 5432 | male | 25 | Shandong University |
+-----------+--------+------+--------------+
1 row in set (0.01 sec)
8、 Comparison operator （3）： Find user information for a certain age group
subject ： To query 20 Years old and older and 23 User information aged and under , Take out the qualified equipment ID、 Gender 、 Age .
User information sheet ：user_profile The data in the table are as follows .
| 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 |
The query should return the following results ：
| device_id | gender | age |
|---|---|---|
| 2138 | male | 21 |
| 6543 | female | 20 |
| 2315 | female | 23 |
answer ：
-- Use between ... and ...
mysql> select device_id, gender, age from user_profile where age between 20 and 23;
+-----------+--------+------+
| device_id | gender | age |
+-----------+--------+------+
| 2138 | male | 21 |
| 6543 | female | 20 |
| 2315 | female | 23 |
+-----------+--------+------+
3 rows in set (0.01 sec)
-- Use comparison operators and logical operators
mysql> select device_id, gender, age from user_profile where age >= 20 and age <= 23;
+-----------+--------+------+
| device_id | gender | age |
+-----------+--------+------+
| 2138 | male | 21 |
| 6543 | female | 20 |
| 2315 | female | 23 |
+-----------+--------+------+
3 rows in set (0.00 sec)
9、 Comparison operator （4）： Find user information except Fudan University
subject ： To view all user information except Fudan University , Take out the device id, Gender , Age , School .
Example ：user_profile The data in the table are as follows .
| 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 |
The query should return the following results ：
| device_id | gender | age | university |
|---|---|---|---|
| 2138 | male | 21 | Peking University, |
| 6543 | female | 20 | Peking University, |
| 2315 | female | 23 | Zhejiang University |
| 5432 | male | 25 | Shandong University |
answer ：
-- Use <>
mysql> select device_id, gender, age, university from user_profile where university <> ' Fudan University ';
+-----------+--------+------+--------------+
| device_id | gender | age | university |
+-----------+--------+------+--------------+
| 2138 | male | 21 | Peking University, |
| 6543 | female | 20 | Peking University, |
| 2315 | female | 23 | Zhejiang University |
| 5432 | male | 25 | Shandong University |
+-----------+--------+------+--------------+
4 rows in set (0.00 sec)
-- Use not
mysql> select device_id, gender, age, university from user_profile where not university = ' Fudan University ';
+-----------+--------+------+--------------+
| device_id | gender | age | university |
+-----------+--------+------+--------------+
| 2138 | male | 21 | Peking University, |
| 6543 | female | 20 | Peking University, |
| 2315 | female | 23 | Zhejiang University |
| 5432 | male | 25 | Shandong University |
+-----------+--------+------+--------------+
4 rows in set (0.00 sec)
10、 Comparison operator （5）： Filter for null values
subject ： To view users whose age is not empty , Take out the user's device ID, Gender , Age , School information .
Example ：user_profile The data in the table are as follows .
| 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 |
The query should return the following results ：
| device_id | gender | age | university |
|---|---|---|---|
| 2138 | male | 21 | Peking University, |
| 6543 | female | 20 | Peking University, |
| 2315 | female | 23 | Zhejiang University |
| 5432 | male | 25 | Shandong University |
answer ：
-- Use age is not null
mysql> select device_id, gender, age, university from user_profile where age is not null;
+-----------+--------+------+--------------+
| device_id | gender | age | university |
+-----------+--------+------+--------------+
| 2138 | male | 21 | Peking University, |
| 6543 | female | 20 | Peking University, |
| 2315 | female | 23 | Zhejiang University |
| 5432 | male | 25 | Shandong University |
+-----------+--------+------+--------------+
4 rows in set (0.00 sec)
-- Use not age is null
mysql> select device_id, gender, age, university from user_profile where not age is null;
+-----------+--------+------+--------------+
| device_id | gender | age | university |
+-----------+--------+------+--------------+
| 2138 | male | 21 | Peking University, |
| 6543 | female | 20 | Peking University, |
| 2315 | female | 23 | Zhejiang University |
| 5432 | male | 25 | Shandong University |
+-----------+--------+------+--------------+
4 rows in set (0.00 sec)
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