This section is used to supplement 3

（1） Create database ：mystudent

（2） establish 3 Data tables ：

        ① Student list （stu）

        ② Employee list （emp）

        ③ Departmental table （dept）

         The design is as follows. Complete the following information for the four tables ：

Table structure ：

# Student list ：stu
mysql> desc stu;
+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| sid    | char(6)     | YES  |     | NULL    |       |
| sname  | varchar(50) | YES  |     | NULL    |       |
| age    | int         | YES  |     | NULL    |       |
| gender | varchar(50) | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

# Employee list ：emp
mysql> desc emp;
+----------+--------------+------+-----+---------+-------+
| Field    | Type         | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| empno    | int          | YES  |     | NULL    |       |
| ename    | varchar(50)  | YES  |     | NULL    |       |
| job      | varchar(50)  | YES  |     | NULL    |       |
| mgr      | int          | YES  |     | NULL    |       |
| hiredate | date         | YES  |     | NULL    |       |
| sal      | decimal(7,2) | YES  |     | NULL    |       |
| comm     | decimal(7,2) | YES  |     | NULL    |       |
| deptno   | int          | YES  |     | NULL    |       |
+----------+--------------+------+-----+---------+-------+
8 rows in set (0.00 sec)

# Departmental table ：dept
mysql> desc dept;
+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| deptno | int         | YES  |     | NULL    |       |
| dname  | varchar(14) | YES  |     | NULL    |       |
| loc    | varchar(13) | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

Table data

mysql> # Student list 
mysql> select * from stu;
+--------+----------+------+--------+
| sid    | sname    | age  | gender |
+--------+----------+------+--------+
| S_1001 | liuYi    |   35 | male   |
| S_1002 | chenEr   |   15 | female |
| S_1003 | zhangSan |   95 | male   |
| S_1004 | liSi     |   65 | female |
| S_1005 | wangWu   |   55 | male   |
| S_1006 | zhaoLiu  |   75 | female |
| S_1007 | sunQi    |   25 | male   |
| S_1008 | zhouBa   |   45 | female |
| S_1009 | wuJiu    |   85 | male   |
| S_1010 | zhengShi |    5 | female |
| S_1011 | xxx      | NULL | NULL   |
| S_1012 | NULL     |   10 | female |
+--------+----------+------+--------+
12 rows in set (0.00 sec)

mysql> # Employee list 
mysql> select * from emp;
+-------+--------+-----------+------+------------+---------+---------+--------+
| empno | ename  | job       | mgr  | hiredate   | sal     | comm    | deptno |
+-------+--------+-----------+------+------------+---------+---------+--------+
|  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800.00 |    NULL |     20 |
|  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     30 |
|  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
|  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975.00 |    NULL |     20 |
|  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
|  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850.00 |    NULL |     30 |
|  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450.00 |    NULL |     10 |
|  7788 | SCOTT  | ANALYST   | 7566 | 1987-04-19 | 3000.00 |    NULL |     20 |
|  7839 | KING   | PRESIDENT | NULL | 1981-11-17 | 5000.00 |    NULL |     10 |
|  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |  200.00 |     30 |
|  7876 | ADAMS  | CLERK     | 7788 | 1987-05-23 | 1100.00 |    NULL |     20 |
|  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950.00 |    NULL |     30 |
|  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000.00 |    NULL |     20 |
|  7934 | MILLER | CLERK     | 7782 | 1982-01-23 | 1300.00 |    NULL |     10 |
|  7988 | LISA   |  Procter & Gamble       | 7782 | 2022-07-22 | 1200.00 |    NULL |     50 |
+-------+--------+-----------+------+------------+---------+---------+--------+
15 rows in set (0.00 sec)

mysql> # Departmental table 
mysql> select * from dept;
+--------+------------+----------+
| deptno | dname      | loc      |
+--------+------------+----------+
|     10 | ACCOUNTING | NEW YORK |
|     20 | RESEARCH   | DALLAS   |
|     30 | SALES      | CHICAGO  |
|     40 | OPERATIONS | BOSTON   |
+--------+------------+----------+
4 rows in set (0.00 sec)

Complete according to the above requirements MySQL Statement writing

# Create database myStudent
CREATE DATABASE IF NOT EXISTS `myStudent`;
# Create student table ：stu
CREATE TABLE stu (
	sid       CHAR(6)      COMMENT ' Student student id ',
	sname     VARCHAR(50)  COMMENT ' The student's name ',
	age       INT          COMMENT ' Student age ',
	gender    VARCHAR(50)  COMMENT ' Student gender '
);
# Add data ： Show the students stu Add data to 
INSERT INTO stu VALUES('S_1001', 'liuYi', 35, 'male');
INSERT INTO stu VALUES('S_1002', 'chenEr', 15, 'female');
INSERT INTO stu VALUES('S_1003', 'zhangSan', 95, 'male');
INSERT INTO stu VALUES('S_1004', 'liSi', 65, 'female');
INSERT INTO stu VALUES('S_1005', 'wangWu', 55, 'male');
INSERT INTO stu VALUES('S_1006', 'zhaoLiu', 75, 'female');
INSERT INTO stu VALUES('S_1007', 'sunQi', 25, 'male');
INSERT INTO stu VALUES('S_1008', 'zhouBa', 45, 'female');
INSERT INTO stu VALUES('S_1009', 'wuJiu', 85, 'male');
INSERT INTO stu VALUES('S_1010', 'zhengShi', 5, 'female');
INSERT INTO stu VALUES('S_1011', 'xxx', NULL, NULL);
INSERT INTO stu VALUES('S_1012', NULL, 10, 'female');


# Create an employee table ：emp
CREATE TABLE emp(
	empno      INT           COMMENT ' Employee number ',
	ename      VARCHAR(50)   COMMENT ' Employee name ',
	job        VARCHAR(50)   COMMENT ' Staff work ',
	mgr        INT           COMMENT ' Led number ',
	hiredate   DATE          COMMENT ' Date of entry ',
	sal        DECIMAL(7,2)  COMMENT ' a monthly salary ',
	comm       DECIMAL(7,2)  COMMENT ' Bonus ',
	deptno     INT           COMMENT ' Department number '
) ;
# Add data ： Report to employees emp Add data to 
INSERT INTO emp VALUES(7369,'SMITH','CLERK',7902,'1980-12-17',800,NULL,20);
INSERT INTO emp VALUES(7499,'ALLEN','SALESMAN',7698,'1981-02-20',1600,300,30);
INSERT INTO emp VALUES(7521,'WARD','SALESMAN',7698,'1981-02-22',1250,500,30);
INSERT INTO emp VALUES(7566,'JONES','MANAGER',7839,'1981-04-02',2975,NULL,20);
INSERT INTO emp VALUES(7654,'MARTIN','SALESMAN',7698,'1981-09-28',1250,1400,30);
INSERT INTO emp VALUES(7698,'BLAKE','MANAGER',7839,'1981-05-01',2850,NULL,30);
INSERT INTO emp VALUES(7782,'CLARK','MANAGER',7839,'1981-06-09',2450,NULL,10);
INSERT INTO emp VALUES(7788,'SCOTT','ANALYST',7566,'1987-04-19',3000,NULL,20);
INSERT INTO emp VALUES(7839,'KING','PRESIDENT',NULL,'1981-11-17',5000,NULL,10);
INSERT INTO emp VALUES(7844,'TURNER','SALESMAN',7698,'1981-09-08',1500,200,30);
INSERT INTO emp VALUES(7876,'ADAMS','CLERK',7788,'1987-05-23',1100,NULL,20);
INSERT INTO emp VALUES(7900,'JAMES','CLERK',7698,'1981-12-03',950,NULL,30);
INSERT INTO emp VALUES(7902,'FORD','ANALYST',7566,'1981-12-03',3000,NULL,20);
INSERT INTO emp VALUES(7934,'MILLER','CLERK',7782,'1982-01-23',1300,NULL,10);

# Create department table ：dept
CREATE TABLE dept(
	deptno INT          COMMENT ' Department number ',
	dname  VARCHAR(14)  COMMENT ' Department name ',
	loc    VARCHAR(13)  COMMENT ' Department Address '
);

INSERT INTO dept VALUES(10, 'ACCOUNTING', 'NEW YORK');
INSERT INTO dept VALUES(20, 'RESEARCH', 'DALLAS');
INSERT INTO dept VALUES(30, 'SALES', 'CHICAGO');
INSERT INTO dept VALUES(40, 'OPERATIONS', 'BOSTON');

Query statement writing order ：select – from- where- group by- having- order by-limit
Query statement execution order ：from - where -group by - having - select - order by-limit

Single table query ：

01、 Basic query

1. Inquire about stu All fields in the table

2. Query the specified column in the student table

02、 Conditions of the query

3. Check gender for female , And older than 50 The record of

4. Check gender for female , And older than 50 Employee number and name

5. The student ID is S_1001, Or the name is lisi The record of

6. The student ID is S_1001,S_1002,S_1003 The record of

7. It's not S_1001,S_1002,S_1003 The record of

8. Query age is null The record of

9. The age of inquiry is 20 To 40 Between student records

10. Check the student records of non male students

11. The search name is not null Student records of

03、 Fuzzy query

12. Search name by 5 Student records in letters

13. Search name by 5 Letter composition , And No 5 The letters are "i" Student records of

14. Check the name with “z” The student record at the beginning

15. Check the number of 2 The letters are “i” Student records of

16. The query name contains “a” The student record of letters

04、 Field control query

17. Remove duplicate records DISTINCT

18. Check the sum of the employee's monthly salary and Commission   Be careful : A number with NULL Carry out operations , The result is NULL

19. Add an alias to the column name , Use As keyword   As Keywords can be omitted

05、 Sort

20. Check all student records , Sort by age in ascending order

21. Check all student records , Sort by age in descending order

22. Check all employees , Sort by monthly salary in descending order , If the monthly salary is the same , Sort by number in ascending order

23. Check all employees , Sort by monthly salary in descending order , If the monthly salary is the same , Sort by number in descending order

24. Check that the salary is higher than 1600 Employee records of , And sort in descending order according to salary

06、 Aggregate functions

25.COUNT()： The specified column of statistics is not NULL The number of record lines

26.MAX(): Calculate the maximum value of the specified column , If the specified column is of string type , So use string sort operation

27.MIN(): Calculate the minimum value of the specified column , If the specified column is of string type , So use string sort operation

28.SUM(): Calculates the value of the specified column and , If the specified column type is not a numeric type , So the result is 0

29.AVG(): Calculate the average value of the specified column , If the specified column type is not a numeric type , So the result is 0

30. Inquire about emp The monthly salary in the table is more than 2500 The number of people

31. The sum of monthly salary and commission is greater than 2500 The number of yuan

32. Check the monthly salary of all employees + Commission and

07、 Group query

33. Query the department number of each department and the salary and

34. Check the department number of each department and the number of people in each department

35. Query the department number of each department and the salary of each department is greater than 1500 The number of people

08、having Clause

36. The total salary is greater than 9000 Department number and salary and

09、limit

37. Inquire about 5 rows , Start with 0 Start

38. Inquire about 10 rows , Start with 3 Start

Multi-table query

01、 Merge result set

02、 Link query