Crud of MySQL

One , Basic additions and deletions

（SQLServer And PLSQL The statements are basically the same ）
Be careful ： however "+" stay MySQL The plus sign inside does not make splicing , Just do arithmetic

select * from t_student
desc t_student
insert into t_student values('01' , ' Zhao Lei ' , '1990-01-01' , ' male ');
 
-- Fuzzy query 
select * from t_student where sname=' Zhao Lei '
 
update t_student set sname='xi' where sid='01'
 
DELETE * FROM t_student where sid = '01';

Two , Case presentation

 Case study 1： Query the employee name and bonus rate without bonus 
SELECT
last_name,
commission_pct
FROM
t_mysql_employees
WHERE
commission_pct IS NULL;
​
​
 Case study 1： Check the name and bonus rate of employees with bonus 
SELECT
last_name,
commission_pct
FROM
t_mysql_employees
WHERE
commission_pct IS NOT NULL;
 
 
 
 Case study 2： Query salary as 12000 Employee information 
SELECT
last_name,
salary
FROM
t_mysql_employees
​
WHERE
salary <=> 12000;
 
 
 
 Add filter criteria and sort 
​
 Case study ： Check department number >=90 Employee information , And in descending order of employee number 
​
SELECT *
FROM t_mysql_employees
WHERE department_id>=90
ORDER BY employee_id DESC;
​
​
3、 Sort by expression 
# Case study ： Query employee information   In descending order of annual salary 
​
​
SELECT *,salary*12*(1+IFNULL(commission_pct,0))
FROM t_mysql_employees
ORDER BY salary*12*(1+IFNULL(commission_pct,0)) DESC;
​
​
 
 
4、 Sort by alias 
 Case study ： Query employee information   In ascending order of annual salary 
​
SELECT *,salary*12*(1+IFNULL(commission_pct,0))  Annual salary 
FROM t_mysql_employees
ORDER BY  Annual salary  ASC;
​
 
 
 
 
5、 Sort by function 
 Case study ： Query employee name , And in descending order of the length of the names 
​
SELECT LENGTH(last_name),last_name
FROM t_mysql_employees
ORDER BY LENGTH(last_name) DESC;
​
 
 
6、 Sort by multiple fields 
 
 Case study ： Query employee information , It is required that the salary be in descending order first , Press again employee_id Ascending 
SELECT *
FROM t_mysql_employees
ORDER BY salary DESC,employee_id ASC;
​

design sketch
Case a ：

Case 2

Case three ：

3、 ... and , Sort expansion

1. Expand one
Code demonstration 1

1. Check the employee's name, department number and annual salary , In descending order of annual salary   Ascending by name 
​
SELECT last_name,department_id,salary*12*(1+IFNULL(commission_pct,0))  Annual salary 
FROM t_mysql_employees
ORDER BY  Annual salary  DESC,last_name ASC;
​

design sketch 1

Code demonstration 2

2. The choice of salary is not in 8000 To 17000 The name and salary of the employee , In descending order of wages 
SELECT last_name,salary
FROM t_mysql_employees
WHERE salary NOT BETWEEN 8000 AND 17000
ORDER BY salary DESC;
​

design sketch 2

Code demonstration 3

3. Query mailbox contains e Employee information , And first by the number of bytes in the mailbox , And then in ascending order by department number 
​
SELECT *,LENGTH(email)
FROM t_mysql_employees
WHERE email LIKE '%e%'
ORDER BY LENGTH(email) DESC,department_id ASC;
​

design sketch 3

2. Development 2
《 Correlation table 》
Code demonstration 1

-- User table 
CREATE TABLE tb_user(
	user_id  VARCHAR(15) NOT NULL,
	order_time datetime not null,
	order_category VARCHAR(20) not null,
	order_amt float not null,
	shop_id VARCHAR(50) not null
)
 
 
insert into tb_user VALUES('D890','2018-01-06 12:34:00',' skewer ',18.90,'ZL123');
insert into tb_user VALUES('D890','2018-02-07 12:34:00',' Hamburger ',19.50,'SM456');
insert into tb_user VALUES('B456','2018-03-06 12:34:00',' Chicken wings ',10.30,'ZL123');
insert into tb_user VALUES('B456','2018-04-01 12:34:00',' Spicy Hot Pot ',25.30,'HBW123');
insert into tb_user VALUES('C789','2018-05-09 12:34:00',' Spicy Hot Pot ',15.78,'XM456');
 
-- Merchant list 
CREATE TABLE tb_db(
	shop_id  VARCHAR(15) NOT NULL,
	db_name VARCHAR(20),
	db_team VARCHAR(20),
	START_time datetime,
	END_time datetime
)
 
 
 
insert into tb_db VALUES('ZL123',' Xiao Ming ',' sales A Group ','2018-01-01','2015-01-14');
insert into tb_db VALUES('ZL123',' Xiao Zhang ',' sales A Group ','2016-01-15','2018-01-17');
insert into tb_db VALUES('SM456',' Xiao Zhang ',' sales B Group ','2016-01-17','2016-01-16');
insert into tb_db VALUES('HBW123',' Xiao Deng ',' sales B Group ','2015-01-01','2017-01-14');
insert into tb_db VALUES('HBW123',' petty thief ',' sales C Group ','2015-01-01','2018-01-15');
insert into tb_db VALUES('XM456',' Xiao Chen ',' sales C Group ','2017-01-01','2019-01-14')

design sketch 1

Code demonstration 2

-- The number of people who only ate spicy hot and hamburgers in January 
select count(*) from(
select count(*) from(
select * from (
select * from tb_user where order_time like '%-01-%'
) c where order_category=' Spicy Hot Pot ' or order_category=' Hamburger '
) d GROUP BY user_id HAVING COUNT(*)=2
) e
 

design sketch 2

Code demonstration 3

-- Calculate each BD_team Of bd Sales of the corresponding stores 
 
select SUM(order_amt) from tb_db a, tb_user b where a.shop_id=b.shop_id GROUP BY a.db_team

design sketch 3