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1：等值連接
     迪卡爾集連接
                  select ename, a.deptno as a_deptno,b.deptno as b_deptno ,b.dname as 部門
                  from emp a, dept b
 
     等值連接
                  select ename, a.deptno as a_deptno,b.deptno as b_deptno ,b.dname as 部門
                  from emp a, dept b
                  where a.deptno = b.deptno;

2：非等值連接，在emp表和salgrade表中查找員工的姓名，工資，等級(jí)，工資上線，工資下線
                 select ename as 姓名, sal as 工資, grade as 工資等級(jí),losal as 工資上線，hisal as 工資下線
                 from emp, salgrade
                 where sal between losal and hisal;

3:外連
       右外連
                 select e.ename, d.dname, e.deptno
                 from emp e,dept d
                 where e.deptno = d.deptno(+);

        左外連與右外連相反

     以hr登陸查詢表employees 和departments 表
                 select  first_name as 姓名, department_name as 部門名稱,  d.department_id as 部門編號(hào) 
                 from employees e, departments d
                 where e.department_id= d.department_id(+) ;

4:自連：在同一個(gè)表中查詢每個(gè)員工及上司的工號(hào)和姓名
                 select a.empno  as 員工編號(hào), a.ename as 員工姓名, a.mgr as 上司的員工編號(hào), b.ename as 上司姓名
                  from emp a, emp b
                 where a.mgr = b.empno;

5：sql99
         交叉連接 cross join------相當(dāng)于迪卡爾集
                  select e.ename,d.dname
                  from emp e cross join dept d;

         自然連接 natural join------相當(dāng)?shù)戎颠B接
                  select e.ename, d.dname
                  from emp e natural join dept d;

         using子句-----使用同名列查詢
              select e.ename, d.dname
              from emp e join dept d
              using (deptno);

         on子句 ------當(dāng)列名不同時(shí)用on子句
              用on查詢兩張表
                   select e.ename, d.dname
                    from emp e join dept d
                   on e.deptno = d.deptno;

      用on查詢多張表
               select e.ename, d.dname
               from emp e join dept d
               on e.deptno = d.deptno
               join 第三個(gè)表
               on 列1 = 列2;

     內(nèi)連接（Inner join）-------內(nèi)連接只返回滿足連接條件的數(shù)據(jù)
              select employee_id, last_name, salary, department_id, department_name
              from employees inner join departments using(department_id);

     左外連
              select employee_id, last_name, salary, department_id, department_name
              from employees left join departments using(department_id);
 
     右外連
              select employee_id, last_name, salary, department_id, department_name
              from employees right join departments using(department_id);

     滿外連
              select employee_id, last_name, salary, department_id, department_name
              from employees full outer join departments using(department_id);

    
    子查詢------------
             查找出工資比scott高的人
              select ename, sal from emp
              where sal>
              (select sal from emp where ename='SCOTT');
 
     查找那些人和scott相同職位的人
              select ename, job from emp
              where job=
               (select job from emp where ename='SCOTT')  
               and ename <> 'SCOTT';

     any的用法  < any意味著小于最大、> any大于最小
              select empno, ename, sal, job
              from emp 
              where sal<any(select sal from emp where job='SALESMAN');

     all的用法 < all：小于所有，即小于最小、> all：大于所有，即大于最大
              select empno, ename, sal, job
              from emp
              where sal<all(select sal from emp where job='SALESMAN');