mysql这篇再看懂一次

-- 创建表的时候 声明外键
create table dept(
	id int primary key auto_increment,
	name varchar(40)
);
insert into dept values (null,'财务部'),(null,'人事部'),(null,'行政部'),(null,'科技部'),(null,'销售部');

create table emp(
	id int primary key auto_increment,
	name varchar(40),
	dept_id int,
	foreign key(dept_id) references dept(id)
);

insert into emp values (null,'奥巴马',1),(null,'萨达姆',2),(null,'哈利波特',4),(null,'火车王',4),(null,'张三丰',6);

update dept set id=6 where name='财务部';



-- 已有表建立外键
create table dept(
	id int primary key auto_increment,
	name varchar(40)
);
create table emp(
	id int primary key auto_increment,
	name varchar(40),
	dept_id int
);

ALTER TABLE emp add CONSTRAINT FK_ID FOREIGN KEY(dept_id) REFERENCES dept(id);


-- #两张表相乘的结果,笛卡尔积查询
select * from dept,emp; 

-- #加入两表的关系
select * from dept,emp where dept.id=emp.dept_id;
-- #这种称为内连接查询(两表都有的) 另一种形式 
select * from dept join emp on dept.id = emp.dept_id;
select * from dept inner join emp on dept.id = emp.dept_id;


-- #左外连接查询
select * from dept left join emp on dept.id = emp.dept_id;

-- #右外连接查询
select * from dept right join emp on dept.id = emp.dept_id;

-- #全外连接查询 full join (mysql不支持)
-- 但是可以间接 利用合并查询
select * from dept left join emp on dept.id = emp.dept_id
union
select * from dept right join emp on dept.id =emp.dept_id;

-- #练习 查询4号部门的名称和其中员工姓名
select dept.name 部门名称,emp.name 员工名称 from dept inner join emp on dept.id = emp.dept_id
where dept.id = 4;



create table department(
	did int(4) not null primary key,
	dname VARCHAR(36)
);

create table employee(
	id int(4) not null primary key,
	name varchar(36),
	age int(2),
	did int(4) not null
);

insert into department values (1,'网络部'),(2,'媒体部'),(3,'研发部'),(4,'人事部');

insert into employee values (1,'王红',20,1),(2,'李强',22,1),(3,'赵四',20,2),(4,'何娟',20,4);


select did from employee where age = 20;

select dname from department where did in (select did from employee where age = 20);

select department.dname from department inner join employee on department.did = employee.did where employee.age = 20;

select dname from department where did not in (select did from employee where age = 20);

select * from department where exists (select * from employee where age > 21);

select * from department where did > any (select did from employee); 





-- #事务
create table account (
	id int not null primary key auto_increment,
	name varchar(20),
	money double
);

insert into account values (1,'a',1000.0),(2,'b',1000.0);

set [session/global] transaction isolation level ...;
select @@tx_isolation;


-- 存储过程
create table student (
	id int(3) primary key auto_increment,
	name varchar(20) not null,
	grade float,
	gender char(2)
);

insert into student (name,grade,gender) values ('tom',60,'男'),('jack',70,'男'),('rose',90,'女'),('lucy',100,'女');

delimiter //
create procedure proc()
BEGIN
 SELECT * from student;
END //
delimiter ;

-- 定义变量
-- 变量的声明要在begin end 之间
declare myvariable int default 100;
set var_name = expr;

delimiter //
create procedure proc3()
BEGIN
declare myvariable int default 100;
 select myvariable;
--  第一个种方式赋值
 set myvariable = myvariable + 20;
 SELECT myvariable;
END //
delimiter ;

-- 第二种方式赋值
select column_name into var_name from table_name;

-- 光标 游标
declare cursor_name cursor for select_statement;
open cursor_name;
fetch cursor_name into var_name;
close cursor_name;

-- 流程控制


-- if
delimiter //
create procedure proc5()
begin 
	declare v varchar(2);
	set v = 'a';
	if v is null then select 'is null';
	else select 'not null';
	end if;
end //
delimiter ;

-- case
delimiter //

create procedure proc6()
BEGIN
	declare v int;
	set v = 2;
	case v 
		when 1 then select 'value is 1';
		when 2 then select 'value is 2';
		else select 'not 1 or 2';
		end case;
END//

-- loop
-- leave 跳出循环(类似break)
-- iterate 再次循环(类似continue)

delimiter //
create procedure doiterate()
begin
	declare p1 int default 0;
	my_loop:loop
		set p1 =p1+1;
		if p1<10 then iterate my_loop;
		elseif p1 > 10 then
end//


--replace
declare id int default 0;
repeat
	set id = id + 1;
	until id>=10;
end repeat;

--while
declare i int default 0;
while i < 10 do 
	set i=i+1;
end while;


-- 查看存储过程
show procedure status;
show procedure status like "%xxx%";
show create procedure proc_name;

-- 修改存储过程的特性