Oracle 10g SQL Fundamentals I(学习笔记二第4-6章)

第四节:
分组函数:
   select [column,]group_function(column),...
       from table
	   where condition
	   group by column
	   order by column;
	   
	select avg(salary) ,max(salary),min(salary),sum(salary)
	   from employees
	   where job_id where '%REP%';
	select min(hire_date),max(hire_date) from employees;
	select count(*) from employees where department_id=50
	select count(commission_pct) from employees
	   where department_id=80;
	select count( distinct department_id)  from employees;
	
	select avg(nvl(commission_pct,0))
	   from employees;
	   
	select department_id dept_id,job_id,sum(salary) 
	   from employees
	   group by department_id,job_id;
	   
	   
	select department_id dept_id,max(salary) 
	   from employees
	   group by department_id
	   having max(salary)>1000
	   order by sum(salary);
	   
	   
第五章:  关联查询
   交叉查询:
   使用Using字句:
	   select empno,ename,dname ,loc from dept join emp 
	     using (deptno);
	   备注两个表中均有deptno列.
	    select e.empno,e.ename,d.dname ,d.loc from dept d join emp  e
	     using (deptno);
   使用自然连接:
     select empno,ename,dname ,loc from dept
	    natural join emp;
	使用On字句连接:
	    select e.empno,e.ename,d.dname ,d.loc 
		  from dept d join emp  e
	      on (e.deptno=d.deptno) ;
	使用on进行自关联
	     select e.last_name emp,m.last_name mgr
		     from employees e join employees m
		      on (e.manager_id=m.employee_id) ;
	带条件的关联:
	     select e.empno,e.ename,d.dname ,d.loc 
		    from dept d join emp  e
	      on (e.deptno=d.deptno)
		  and e.deptno=24;
	使用on多个表关联
	     select employee_id,city,department_name
		    from employees e
			join departments d
				on d.department_id =e.department_id
			join locations l on d.location_id=l.location_id;
	
	使用on作为条件的非连接用法
	    select last_name,e.salary ,j.grade_level
		  from employees e join job_grades j
		  on e.salary 
		    between j.lowest_sal and j.highest_sal;
		
		左外连接:
		   select e.last_name,e.department_id,d.department_name
		      from employees e left outer join departments d
			  on( e.department_id=d.department_id);
		右外连接
		   select e.last_name,e.department_id,d.department_name
		      from employees e right outer join departments d
			  on( e.department_id=d.department_id);
		全外连接:
		   select e.last_name,e.department_id,d.department_name
		      from employees e full outer join departments d
			  on( e.department_id=d.department_id);
	    
		笛卡儿积形成原因:
		    1.连接的条件的无效.
			2.连接的条件遗漏
			3.两表记录交叉连接.
			
	第六章子查询
	       select last_name,job_id,salary from employees
		   where job_id =(
				select job_id 
				from employees 
				where employee_id=141
			) and salary > (
			       select salary 
				   from employees 
				   where employee_id=143
			)
		带函数的子查询
			select last_name,job_id,salary from employees
			where salary=(select min(salary) from employees);
	    带having条件的子查询
		   select deparment_id,min(salary) 
		   from employees
		   group by department_id 
		   having min(salary)>
		     (
			    select min(salary) from employees 
				where department_id=50
			 );
		使用any操作
			   select employee_id,last_name,job_id,salary
			    from employees 
				where salary< any(
				    select salary from employees
					where job_id ='IT_PROG'
				  )
				  and job_id<> 'IT_PROG';
		使用all操作
			   select employee_id,last_name,job_id,salary
			    from employees 
				where salary< all(
				    select salary from employees
					where job_id ='IT_PROG'
				  )
				  and job_id<> 'IT_PROG';