sqlserver查詢（子查詢，全鏈接，等值鏈接，天然鏈接，左右連，交集，並集，差集）

--部門表

create table dept(

   deptno int primary key,--部門編號

   dname nvarchar(30),--部門名

   loc nvarchar(30)--地址

);

 

--僱員表

create table emp(

   empno int primary key,--僱員號

   ename nvarchar(30),--員工姓名

   job   nvarchar(30),--僱員工做

   mrg int,--僱員上級

   hiredate datetime,--入職時間

   sal numeric(10,2),--薪水

   comm numeric(10,2),--獎金

   deptno int foreign key references dept(deptno)--設置外鍵

);

 

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);

 

子查詢

■什麼是子查詢

子查詢是指嵌入在其它sql語句中的select語句,也叫嵌套查詢

 

■單行子查詢

單行子查詢是指只返回一行數據的子查詢語句

 

請思考：如何顯示與SMITH同一部門的全部員工?

select * from emp where deptno=(select deptno from emp where ename=’SMITH’);

多行子查詢

多行子查詢指返回多行數據的子查詢

請思考:如何查詢和部門的工做相同的僱員的名字、崗位、工資、部門號

1，先查詢10 號部門有哪些崗位

select distinct job from emp where deptno=10;

2，顯示和他的崗位有一個相同的員工

select ename,job,sal,deptno from emp where job in(select distinct job from emp where deptno=10)

 

全鏈接

select * from emp,dept;

天然查詢

天然鏈接:將等值鏈接中的重複列去掉

select student.sno,sname,ssex,sage,sdept,cno,grade from student,sc where student.sno=sc.sno;

左鏈接和右鏈接

左鏈接:left on, 依次遍歷左邊這個表，查詢在右表中是否有對應的記錄,若是有對應記錄,則匹配,不然顯示null

select student.sno,sname,ssex,sage,sdept,cno,grade from student left join sc on(student.sno=sc.sno);

 

右鏈接:rigth on,以右邊的表爲參照

select student.sno,sname,ssex,sage,sdept,cno,grade from student right join sc on(student.sno=sc.sno);

 

union並集

該操做符用於取得兩個結果集的並集。當使用該操做符時，會自動去掉結果集中重複行。

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

 

 

 對兩個結果集進行「union」,"intersecrt","except"運算這兩個結果集的列數必須相同.

intersect交集

使用該操做符用於取得兩個結果集的交集。

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

使用該操做符用於取得兩個結果集的差集，它只會顯示存在第一個集合中，而不存在第二個集合中的數據。

 

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