--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 
