--部门表 create table dept( deptno int primary key,--部门编号 dname nvarchar(30),--部门名 loc nvarchar(30)--地址 ); --雇员表 create table emp( empno int primary key,--雇员号 ename nvarchar(30),--员工姓名 job nvarchar(30),--雇员工作 mrg int,--雇员上级 hiredate datetime,--入职时间 sal numeric(10,2),--薪水 comm numeric(10,2),--奖金 deptno int foreign key references dept(deptno)--设置外键 ); 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'); insert into emp values (7369,'smith','clerk',7902,'1980-12-17',800.00,null,20); insert into emp values(7499,'allen','salesman',7698,'1981-2-20',1600.00,300.00,30); insert into emp values(7521,'ward','salesman',7698,'1981-2-22',1250.00,500.00,30); insert into emp values(7566,'jones','manager',7839,'1981-4-2',2975.00,null,20); insert into emp values(7654,'martin','salesman',7698,'1981-9-28',1250.00,1400.00,30); insert into emp values(7698,'blake','manager',7839,'1981-5-1',2850.00,null,30); insert into emp values(7782,'clark','manager',7839,'1981-6-9',2450.00,null,10); insert into emp values(7788,'scott','analyst',7566,'1987-4-19',3000.00,null,20); insert into emp values(7839,'king','president',null,'1981-11-17',5000.00,null,10); insert into emp values(7844,'turner','salesman',7698,'1981-9-8',1500.00,0.00,30); insert into emp values(7876,'adams','clerk',7788,'1987-5-23',1100.00,null,20); insert into emp values(7900,'james','clerk',7698,'1981-12-3',950.00,null,30); insert into emp values(7902,'ford','analyst',7566,'1981-12-3',3000.00,null,20); insert into emp values(7934,'miller','clerk',7782,'1982-1-23',1300.00,null,10);
子查询
■什么是子查询
子查询是指嵌入在其它sql语句中的select语句,也叫嵌套查询
■单行子查询
单行子查询是指只返回一行数据的子查询语句
请思考：如何显示与smith同一部门的所有员工?
select * from emp where deptno=(select deptno from emp where ename=’smith’);
多行子查询
多行子查询指返回多行数据的子查询
请思考:如何查询和部门的工作相同的雇员的名字、岗位、工资、部门号
1，先查询10 号部门有哪些岗位
select distinct job from emp where deptno=10;
2，显示和他的岗位有一个相同的员工
select ename,job,sal,deptno from emp where job in(select distinct job from emp where deptno=10)
全连接
select * from emp,dept;
自然查询
自然连接:将等值连接中的重复列去掉 select student.sno,sname,ssex,sage,sdept,cno,grade from student,sc where student.sno=sc.sno;
左连接和右连接
左连接:left on, 依次遍历左边这个表，查询在右表中是否有对应的记录,如果有对应记录,则匹配,否则显示null select student.sno,sname,ssex,sage,sdept,cno,grade from student left join sc on(student.sno=sc.sno); 右连接:rigth on,以右边的表为参照 select student.sno,sname,ssex,sage,sdept,cno,grade from student right join sc on(student.sno=sc.sno);
union并集
该操作符用于取得两个结果集的并集。当使用该操作符时，会自动去掉结果集中重复行。
select ename,sal,job from emp where sal>2500 union select ename,sal,job from emp where job='manager';
select * from student where sage>20 union select * from student where sage<22
对两个结果集进行“union”,”intersecrt”,”except”运算这两个结果集的列数必须相同.
intersect交集
使用该操作符用于取得两个结果集的交集。
select ename,sal,job from emp where sal>2500 intersect select ename,sal,job from emp where job='manager';
select * from student where sage>20 intersect select * from student where sage<22
except差集
使用该操作符用于取得两个结果集的差集，它只会显示存在第一个集合中，而不存在第二个集合中的数据。
select ename,sal,job from emp where sal>2500 minus select ename,sal,job from emp where job='manager';
select * from student where sage>20 except select * from student where sage>22