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+笔记
+
+```sql
+事务的特性
+原子性 一致性 隔离性 持久性
+事务分为隐式事务和显式事务
+## 方法1：通过set autocommit = 0关闭事务自动提交
+# 查询是否开启事务自动提交，1：事务自动提交；2：事务不自动提交
+SELECT @@autocommit;
+# 关闭事务自动提交
+SET autocommit = 0;
+## 方法2：  START TRANSACTION命令
+# 开启一个事务，使用这个命令之后，事务要使用commit或者commit work命令才会提交
+START TRANSACTION;
+只读事务
+start transaction read only;
+
+savepoint关键字
+可以将一大批操作分为几个部分，然后指定回滚某个部分。可以使用savepoin来实现
+
+隔离级别分为4种：
+读未提交：READ-UNCOMMITTED
+读已提交：READ-COMMITTED
+可重复读：REPEATABLE-READ
+串行：SERIALIZABLE
+```
+
+```sql
+create table dept1(
+	deptno int primary key auto_increment, -- 部门编号
+	dname varchar(14) ,	  -- 部门名字
+	loc varchar(13)   -- 地址
+) ;
+
+
+insert into dept1 values(10,'财务部','北京');
+insert into dept1 values(20,'研发部','上海');
+insert into dept1 values(30,'销售部','广州');
+insert into dept1 values(40,'行政部','深圳');
+
+SELECT * FROM dept1;
+
+set autocommit=0;
+
+DELETE FROM dept1 WHERE deptno in(10,20);
+
+ROLLBACK;
+
+COMMIT;
+
+start transaction;
+
+SAVEPOINT d1;
+
+DELETE FROM dept1 WHERE deptno=30;
+
+ROLLBACK to d1;
+
+start transaction read only;
+```
+
+```sql
+CREATE DATABASE a charset utf8;
+use a;
+
+-- 部门表
+create table dept(
+	deptno int primary key auto_increment, -- 部门编号
+	dname varchar(14) ,	  -- 部门名字
+	loc varchar(13)   -- 地址
+) ;
+-- 员工表
+create table emp(
+	empno int primary key auto_increment,-- 员工编号
+	ename varchar(10), -- 员工姓名										-
+	job varchar(9),	-- 岗位
+	mgr int,	 -- 直接领导编号
+	hiredate date, -- 雇佣日期，入职日期
+	sal int, -- 薪水
+	comm int,  -- 提成
+	deptno int not null, -- 部门编号
+	foreign key (deptno) references dept(deptno)
+);
+insert into dept values(10,'财务部','北京');
+insert into dept values(20,'研发部','上海');
+insert into dept values(30,'销售部','广州');
+insert into dept values(40,'行政部','深圳');
+insert into emp values(7369,'刘一','职员',7902,'1980-12-17',800,null,20);
+insert into emp values(7499,'陈二','推销员',7698,'1981-02-20',1600,300,30);
+insert into emp values(7521,'张三','推销员',7698,'1981-02-22',1250,500,30);
+insert into emp values(7566,'李四','经理',7839,'1981-04-02',2975,null,20);
+insert into emp values(7654,'王五','推销员',7698,'1981-09-28',1250,1400,30);
+insert into emp values(7698,'赵六','经理',7839,'1981-05-01',2850,null,30);
+insert into emp values(7782,'孙七','经理',7839,'1981-06-09',2450,null,10);
+insert into emp values(7788,'周八','分析师',7566,'1987-06-13',3000,null,20);
+insert into emp values(7839,'吴九','总裁',null,'1981-11-17',5000,null,10);
+insert into emp values(7844,'郑十','推销员',7698,'1981-09-08',1500,0,30);
+insert into emp values(7876,'郭十一','职员',7788,'1987-06-13',1100,null,20);
+insert into emp values(7900,'钱多多','职员',7698,'1981-12-03',950,null,30);
+insert into emp values(7902,'大锦鲤','分析师',7566,'1981-12-03',3000,null,20);
+insert into emp values(7934,'木有钱','职员',7782,'1983-01-23',1300,null,10);
+
+
+
+
+
+-- 1、列出最低薪金大于1500的各种工作。
+-- 
+SELECT empno FROM emp WHERE sal>1500 
+SELECT job,min(sal) FROM emp WHERE empno in(SELECT empno FROM emp WHERE sal>1500 
+) GROUP BY job
+-- 2、列出在部门 "销售部" 工作的员工的姓名，假定不知道销售部的部门编号。
+-- 
+SELECT deptno FROM dept WHERE dname='销售部'
+SELECT ename FROM emp WHERE deptno in(SELECT deptno FROM dept WHERE dname='销售部'
+);
+-- 3、列出薪金高于公司平均薪金的所有员工。
+-- 
+SELECT avg(sal) FROM emp;
+SELECT ename,sal FROM emp HAVING sal>(SELECT avg(sal) FROM emp
+)
+-- 4、列出与"周八"从事相同工作的所有员工。
+-- 
+SELECT job FROM emp WHERE ename='周八'
+
+SELECT * FROM emp WHERE job in(SELECT job FROM emp WHERE ename='周八'
+);
+-- 5、列出薪金等于部门30中员工的薪金的所有员工的姓名和薪金。
+-- 
+SELECT sal FROM emp WHERE deptno=30
+SELECT ename,sal FROM emp WHERE sal in(SELECT sal FROM emp WHERE deptno=30
+)and deptno!=30;
+-- 6、列出薪金高于在部门30工作的所有员工的薪金的员工姓名和薪金。
+-- 
+SELECT emp.ename,emp.sal FROM emp WHERE emp.sal >(SELECT max(sal) FROM emp WHERE deptno=30
+)and emp.deptno!=30;
+-- 7、列出在每个部门工作的员工数量、平均工资、平均服务年限。
+-- 
+SELECT count(empno),avg(DATEDIFF(NOW(),hiredate))/365,avg(sal) FROM emp right join dept on emp.deptno=dept.deptno GROUP BY dname
+-- 8、列出所有员工的姓名、部门名称和工资。
+-- 
+SELECT ename,dname,sal FROM emp right join dept on emp.deptno=dept.deptno 
+
+-- 9、列出所有部门的详细信息和部门人数。
+-- 
+SELECT dept.*,count(empno) FROM emp right join dept on emp.deptno=dept.deptno GROUP BY deptno
+
+-- 10、列出各种工作的最低工资。
+-- 
+SELECT job,min(sal) FROM emp GROUP BY job;
+-- 11、列出各个部门的 经理 的最低薪金。
+-- 
+select deptno,min(sal)  from emp  where job="经理" group by deptno;
+-- 12、列出所有员工的年工资,按年薪从低到高排序。 
+select ename,(sal+ifnull(comm,0))*12 yearsal from emp order by yearsal;
+
+
+```