sqlserver queries (subqueries, fully connected, the equivalent connection, natural connection, even around the intersection, union, difference)

- the department table 

the Create  the Table the dept ( 

   deptno int  Primary  Key , - department number 

   DNAME nvarchar ( 30 ), - a department name 

   LOC nvarchar ( 30 ) - address 

); 

 

- Employee table 

the Create  the Table emp ( 

   empno int  Primary  Key , - employee number 

   ename nvarchar ( 30 ), - employee name 

   the Job    nvarchar ( 30), - employees work 

   MRG int , - the employee the higher 

   the HireDate datetime , - entry time 

   SAL numeric ( 10 , 2 ), - salaries 

   COMM numeric ( 10 , 2 ), - bonuses 

   deptno int  Foreign  Key  the References the dept (deptno ) - foreign key 

); 

 

INSERT  INTO Dept values ( 10 , ' the 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);

Subqueries

■ What is a subquery

Subquery is a sql statement embedded in other select statement, also called nested query

■ single-row subquery

Single-row subquery returns only one row of data refers to a sub-query

Consider: how to display all the employees in the same department SMITH?

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

Multiple-row subqueries

Multi-line sub-query returns multiple rows of data refers to a sub-query

Consider: how to query and name of the same department employee, job, salary, department number

1, first check what post No. 10 departments

select distinct job from emp where deptno=10;

2, displaying his post and have a same employee

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

Fully connected

select * from emp,dept;

Natural query

Natural join: the equivalent Duplicate column removed 

SELECT student.sno, sname, SSEx, SAGE, sdept, CNO, Grade from Student, SC WHERE student.sno = sc.sno;

Left and right connections

Left connection: left  ON , turn left to traverse the table, the query whether there are corresponding records in the right table, if there is a corresponding record, the match or the display null 

the SELECT student.sno, sname, SSEx, SAGE, sdept, CNO, Grade from Student left  the Join SC ON (student.sno = sc.sno); 

 

right connection: rigth ON , the right side as a reference in table 

SELECT student.sno, sname, SSEx, SAGE, sdept, CNO, Grade from Student right  the Join SC ON (student.sno = sc.sno);

union union

The operator is used to achieve the result set and two sets. When using this operator, the result set will automatically remove duplicates.

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

Two sets of results " Union", "intersecrt", "the except" operation of these two columns of the result set must be the same .

intersect intersection

Using the operator for acquiring the intersection of two sets of results.

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 difference set

Using the operator for obtaining the difference between two sets of result sets, it will only show the presence of the first set, the second set of data is not present.

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