Oracle数据库多表查询之多表连接基本查询
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本文依赖之前两篇文章
/*
多表查询
什么是笛卡尔积？
emp表14行，dept表4行，笛卡尔积：14*4=56行
*/
/*
Oracle的连接条件的类型
等值连接
不等值连接
外连接
自连接
*/
/*
多表连接示例
1、多表连接基本查询
使用一张以上的表做查询就是多表查询
*/
-- 查询员工表和部门表
select * from emp,dept;
/* 查询结果 */
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO DEPTNO DNAME LOC
----- ---------- --------- ----- ----------- --------- --------- ------ ------ -------------- -------------
7369 SMITH CLERK 7902 1980/12/17 800.00 20 10 ACCOUNTING NEW YORK
7499 ALLEN SALESMAN 7698 1981/02/20 1600.00 300.00 30 10 ACCOUNTING NEW YORK
7521 WARD SALESMAN 7698 1981/02/22 1250.00 500.00 30 10 ACCOUNTING NEW YORK
7566 JONES MANAGER 7839 1981/04/02 2975.00 20 10 ACCOUNTING NEW YORK
7654 MARTIN SALESMAN 7698 1981/09/28 1250.00 1400.00 30 10 ACCOUNTING NEW YORK
7698 BLAKE MANAGER 7839 1981/05/01 2850.00 30 10 ACCOUNTING NEW YORK
7782 CLARK MANAGER 7839 1981/06/09 2450.00 10 10 ACCOUNTING NEW YORK
7788 SCOTT ANALYST 7566 1987/04/19 3000.00 20 10 ACCOUNTING NEW YORK
7839 KING PRESIDENT 1981/11/17 5000.00 10 10 ACCOUNTING NEW YORK
7844 TURNER SALESMAN 7698 1981/09/08 1500.00 0.00 30 10 ACCOUNTING NEW YORK
7876 ADAMS CLERK 7788 1987/05/23 1100.00 20 10 ACCOUNTING NEW YORK
7900 JAMES CLERK 7698 1981/12/03 950.00 30 10 ACCOUNTING NEW YORK
7902 FORD ANALYST 7566 1981/12/03 3000.00 20 10 ACCOUNTING NEW YORK
7934 MILLER CLERK 7782 1982/01/23 1300.00 10 10 ACCOUNTING NEW YORK
7369 SMITH CLERK 7902 1980/12/17 800.00 20 20 RESEARCH DALLAS
7499 ALLEN SALESMAN 7698 1981/02/20 1600.00 300.00 30 20 RESEARCH DALLAS
7521 WARD SALESMAN 7698 1981/02/22 1250.00 500.00 30 20 RESEARCH DALLAS
7566 JONES MANAGER 7839 1981/04/02 2975.00 20 20 RESEARCH DALLAS
7654 MARTIN SALESMAN 7698 1981/09/28 1250.00 1400.00 30 20 RESEARCH DALLAS
7698 BLAKE MANAGER 7839 1981/05/01 2850.00 30 20 RESEARCH DALLAS
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO DEPTNO DNAME LOC
----- ---------- --------- ----- ----------- --------- --------- ------ ------ -------------- -------------
7782 CLARK MANAGER 7839 1981/06/09 2450.00 10 20 RESEARCH DALLAS
7788 SCOTT ANALYST 7566 1987/04/19 3000.00 20 20 RESEARCH DALLAS
7839 KING PRESIDENT 1981/11/17 5000.00 10 20 RESEARCH DALLAS
7844 TURNER SALESMAN 7698 1981/09/08 1500.00 0.00 30 20 RESEARCH DALLAS
7876 ADAMS CLERK 7788 1987/05/23 1100.00 20 20 RESEARCH DALLAS
7900 JAMES CLERK 7698 1981/12/03 950.00 30 20 RESEARCH DALLAS
7902 FORD ANALYST 7566 1981/12/03 3000.00 20 20 RESEARCH DALLAS
7934 MILLER CLERK 7782 1982/01/23 1300.00 10 20 RESEARCH DALLAS
7369 SMITH CLERK 7902 1980/12/17 800.00 20 30 SALES CHICAGO
7499 ALLEN SALESMAN 7698 1981/02/20 1600.00 300.00 30 30 SALES CHICAGO
7521 WARD SALESMAN 7698 1981/02/22 1250.00 500.00 30 30 SALES CHICAGO
7566 JONES MANAGER 7839 1981/04/02 2975.00 20 30 SALES CHICAGO
7654 MARTIN SALESMAN 7698 1981/09/28 1250.00 1400.00 30 30 SALES CHICAGO
7698 BLAKE MANAGER 7839 1981/05/01 2850.00 30 30 SALES CHICAGO
7782 CLARK MANAGER 7839 1981/06/09 2450.00 10 30 SALES CHICAGO
7788 SCOTT ANALYST 7566 1987/04/19 3000.00 20 30 SALES CHICAGO
7839 KING PRESIDENT 1981/11/17 5000.00 10 30 SALES CHICAGO
7844 TURNER SALESMAN 7698 1981/09/08 1500.00 0.00 30 30 SALES CHICAGO
7876 ADAMS CLERK 7788 1987/05/23 1100.00 20 30 SALES CHICAGO
7900 JAMES CLERK 7698 1981/12/03 950.00 30 30 SALES CHICAGO
7902 FORD ANALYST 7566 1981/12/03 3000.00 20 30 SALES CHICAGO
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO DEPTNO DNAME LOC
----- ---------- --------- ----- ----------- --------- --------- ------ ------ -------------- -------------
7934 MILLER CLERK 7782 1982/01/23 1300.00 10 30 SALES CHICAGO
7369 SMITH CLERK 7902 1980/12/17 800.00 20 40 OPERATIONS BOSTON
7499 ALLEN SALESMAN 7698 1981/02/20 1600.00 300.00 30 40 OPERATIONS BOSTON
7521 WARD SALESMAN 7698 1981/02/22 1250.00 500.00 30 40 OPERATIONS BOSTON
7566 JONES MANAGER 7839 1981/04/02 2975.00 20 40 OPERATIONS BOSTON
7654 MARTIN SALESMAN 7698 1981/09/28 1250.00 1400.00 30 40 OPERATIONS BOSTON
7698 BLAKE MANAGER 7839 1981/05/01 2850.00 30 40 OPERATIONS BOSTON
7782 CLARK MANAGER 7839 1981/06/09 2450.00 10 40 OPERATIONS BOSTON
7788 SCOTT ANALYST 7566 1987/04/19 3000.00 20 40 OPERATIONS BOSTON
7839 KING PRESIDENT 1981/11/17 5000.00 10 40 OPERATIONS BOSTON
7844 TURNER SALESMAN 7698 1981/09/08 1500.00 0.00 30 40 OPERATIONS BOSTON
7876 ADAMS CLERK 7788 1987/05/23 1100.00 20 40 OPERATIONS BOSTON
7900 JAMES CLERK 7698 1981/12/03 950.00 30 40 OPERATIONS BOSTON
7902 FORD ANALYST 7566 1981/12/03 3000.00 20 40 OPERATIONS BOSTON
7934 MILLER CLERK 7782 1982/01/23 1300.00 10 40 OPERATIONS BOSTON
56 rows selected
/*
56条记录，emp表14条，dept表4条，56条正是emp表和dept表的记录数的乘积，称其为笛卡尔积。
如果多张表进行一起查询而且每张表的数据很大的话，笛卡尔积就会变得非常大，对其性能造成影响，
想去掉笛卡尔积，就需要我们使用关联查询。
*/
-- emp员工表
select * from emp;
/* 查询结果 */
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
----- ---------- --------- ----- ----------- --------- --------- ------
7369 SMITH CLERK 7902 1980/12/17 800.00 20
7499 ALLEN SALESMAN 7698 1981/02/20 1600.00 300.00 30
7521 WARD SALESMAN 7698 1981/02/22 1250.00 500.00 30
7566 JONES MANAGER 7839 1981/04/02 2975.00 20
7654 MARTIN SALESMAN 7698 1981/09/28 1250.00 1400.00 30
7698 BLAKE MANAGER 7839 1981/05/01 2850.00 30
7782 CLARK MANAGER 7839 1981/06/09 2450.00 10
7788 SCOTT ANALYST 7566 1987/04/19 3000.00 20
7839 KING PRESIDENT 1981/11/17 5000.00 10
7844 TURNER SALESMAN 7698 1981/09/08 1500.00 0.00 30
7876 ADAMS CLERK 7788 1987/05/23 1100.00 20
7900 JAMES CLERK 7698 1981/12/03 950.00 30
7902 FORD ANALYST 7566 1981/12/03 3000.00 20
7934 MILLER CLERK 7782 1982/01/23 1300.00 10
14 rows selected
-- dept部门表
select * from dept;
/* 查询结果 */
DEPTNO DNAME LOC
------ -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
/*
emp表和dept表都有一个共同的字段就是deptno，deptno就是两张表的关联字段，
可以使用这个字段做限制条件，两张表的关联查询字段一般是其中一张表的主键，另外一张表的外键。
*/
-- 两表关联查询
select * from emp e,dept d where e.deptno=d.deptno;
/* 查询结果 */
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO DEPTNO DNAME LOC
----- ---------- --------- ----- ----------- --------- --------- ------ ------ -------------- -------------
7782 CLARK MANAGER 7839 1981/06/09 2450.00 10 10 ACCOUNTING NEW YORK
7839 KING PRESIDENT 1981/11/17 5000.00 10 10 ACCOUNTING NEW YORK
7934 MILLER CLERK 7782 1982/01/23 1300.00 10 10 ACCOUNTING NEW YORK
7566 JONES MANAGER 7839 1981/04/02 2975.00 20 20 RESEARCH DALLAS
7902 FORD ANALYST 7566 1981/12/03 3000.00 20 20 RESEARCH DALLAS
7876 ADAMS CLERK 7788 1987/05/23 1100.00 20 20 RESEARCH DALLAS
7369 SMITH CLERK 7902 1980/12/17 800.00 20 20 RESEARCH DALLAS
7788 SCOTT ANALYST 7566 1987/04/19 3000.00 20 20 RESEARCH DALLAS
7521 WARD SALESMAN 7698 1981/02/22 1250.00 500.00 30 30 SALES CHICAGO
7844 TURNER SALESMAN 7698 1981/09/08 1500.00 0.00 30 30 SALES CHICAGO
7499 ALLEN SALESMAN 7698 1981/02/20 1600.00 300.00 30 30 SALES CHICAGO
7900 JAMES CLERK 7698 1981/12/03 950.00 30 30 SALES CHICAGO
7698 BLAKE MANAGER 7839 1981/05/01 2850.00 30 30 SALES CHICAGO
7654 MARTIN SALESMAN 7698 1981/09/28 1250.00 1400.00 30 30 SALES CHICAGO
14 rows selected
/*
可以看到关联之后查询数据是14条，不再是56条
*/
-- 范例1：查询出雇员的编号、姓名，部门的编号、名称和地址
select e.empno,e.ename,d.deptno,d.dname,d.loc from emp e,dept d where e.deptno=d.deptno;
/* 查询结果 */
EMPNO ENAME DEPTNO DNAME LOC
----- ---------- ------ -------------- -------------
7782 CLARK 10 ACCOUNTING NEW YORK
7839 KING 10 ACCOUNTING NEW YORK
7934 MILLER 10 ACCOUNTING NEW YORK
7566 JONES 20 RESEARCH DALLAS
7902 FORD 20 RESEARCH DALLAS
7876 ADAMS 20 RESEARCH DALLAS
7369 SMITH 20 RESEARCH DALLAS
7788 SCOTT 20 RESEARCH DALLAS
7521 WARD 30 SALES CHICAGO
7844 TURNER 30 SALES CHICAGO
7499 ALLEN 30 SALES CHICAGO
7900 JAMES 30 SALES CHICAGO
7698 BLAKE 30 SALES CHICAGO
7654 MARTIN 30 SALES CHICAGO
14 rows selected
-- 范例2：查询出每个员工的上级领导
select e1.empno,e1.ename,e2.empno,e2.ename from emp e1,emp e2 where e1.mgr=e2.empno;
/* 查询结果 */
EMPNO ENAME EMPNO ENAME
----- ---------- ----- ----------
7902 FORD 7566 JONES
7788 SCOTT 7566 JONES
7844 TURNER 7698 BLAKE
7499 ALLEN 7698 BLAKE
7521 WARD 7698 BLAKE
7900 JAMES 7698 BLAKE
7654 MARTIN 7698 BLAKE
7934 MILLER 7782 CLARK
7876 ADAMS 7788 SCOTT
7698 BLAKE 7839 KING
7566 JONES 7839 KING
7782 CLARK 7839 KING
7369 SMITH 7902 FORD
13 rows selected
/*
where e1.mgr=e2.empno 这个条件值得思考
先看一下 where e1.empno=e2.empno
*/
select * from emp e1,emp e2 where e1.empno=e2.empno;
/*
e1相当于员工表，e2相当于上级表；也就是说e1里面的mgr要等于e2里面的empno；
员工表里面的上级等于上级表里面的员工编号。
这就是where e1.mgr=e2.empno
*/
/* 起个别名 */
select e1.empno,e1.ename,e2.empno bossno,e2.ename bossname from emp e1,emp e2 where e1.mgr=e2.empno;
/* 查询结果 */
EMPNO ENAME BOSSNO BOSSNAME
----- ---------- ------ ----------
7902 FORD 7566 JONES
7788 SCOTT 7566 JONES
7844 TURNER 7698 BLAKE
7499 ALLEN 7698 BLAKE
7521 WARD 7698 BLAKE
7900 JAMES 7698 BLAKE
7654 MARTIN 7698 BLAKE
7934 MILLER 7782 CLARK
7876 ADAMS 7788 SCOTT
7698 BLAKE 7839 KING
7566 JONES 7839 KING
7782 CLARK 7839 KING
7369 SMITH 7902 FORD
/* 注意：KING是大boss，其余是他的员工 */
-- 范例3：在范例2“查询出每个员工的上级领导”的基础上，查询该员工的部门名称
select e1.empno,e1.ename,e2.empno bossno,e2.ename bossname,d.dname from emp e1,emp e2,dept d where e1.mgr=e2.empno and e1.deptno=d.deptno;
/* 查询结果 */
EMPNO ENAME BOSSNO BOSSNAME DNAME
----- ---------- ----- ---------- --------------
7902 FORD 7566 JONES RESEARCH
7788 SCOTT 7566 JONES RESEARCH
7521 WARD 7698 BLAKE SALES
7844 TURNER 7698 BLAKE SALES
7654 MARTIN 7698 BLAKE SALES
7499 ALLEN 7698 BLAKE SALES
7900 JAMES 7698 BLAKE SALES
7934 MILLER 7782 CLARK ACCOUNTING
7876 ADAMS 7788 SCOTT RESEARCH
7698 BLAKE 7839 KING SALES
7566 JONES 7839 KING RESEARCH
7782 CLARK 7839 KING ACCOUNTING
7369 SMITH 7902 FORD RESEARCH
13 rows selected
-- 查询工资表
select * from salgrade;
/* 查询结果 */
GRADE LOSAL HISAL
---------- ---------- ----------
1 700 1200
2 1201 1400
3 1401 2000
4 2001 3000
5 3001 9999
-- 范例：查询出每个员工编号、姓名、部门名称、工资等级和他的上级领导的姓名、工资等级。
select e1.empno,e1.ename,d.dname,decode(s1.grade,
1,'一级',
2,'二级',
3,'三级',
4,'四级',
5,'五级') grade,
e2.empno,e2.ename,decode(s2.grade,
1,'一级',
2,'二级',
3,'三级',
4,'四级',
5,'五级') grade
from emp e1,emp e2,dept d,salgrade s1, salgrade s2
where e1.mgr=e2.empno
and e1.deptno=d.deptno
and e1.sal between s1.losal and s1.hisal
and e2.sal between s2.losal and s2.hisal;
/* 查询结果 */
EMPNO ENAME DNAME GRADE EMPNO ENAME GRADE
----- ---------- -------------- ----- ----- ---------- -----
7566 JONES RESEARCH 四级 7839 KING 五级
7698 BLAKE SALES 四级 7839 KING 五级
7782 CLARK ACCOUNTING 四级 7839 KING 五级
7876 ADAMS RESEARCH 一级 7788 SCOTT 四级
7369 SMITH RESEARCH 一级 7902 FORD 四级
7788 SCOTT RESEARCH 四级 7566 JONES 四级
7902 FORD RESEARCH 四级 7566 JONES 四级
7654 MARTIN SALES 二级 7698 BLAKE 四级
7521 WARD SALES 二级 7698 BLAKE 四级
7499 ALLEN SALES 三级 7698 BLAKE 四级
7844 TURNER SALES 三级 7698 BLAKE 四级
7900 JAMES SALES 一级 7698 BLAKE 四级
7934 MILLER ACCOUNTING 二级 7782 CLARK 四级
13 rows selected
-- 查询用户表
select * from user_tables;
/*
外连接（左右连接）
右连接
在做基本连接查询时，查询所有部门下的员工
发现部门编号为40的下面没有员工
*/
-- 部门表
select * from dept;
/* 查询结果 */
DEPTNO DNAME LOC
------ -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
-- 查询所有部门下的员工
select e.empno,e.ename,d.deptno,d.dname
from emp e,dept d
where e.deptno=d.deptno;
/* 查询结果 */
EMPNO ENAME DEPTNO DNAME
----- ---------- ------ --------------
7782 CLARK 10 ACCOUNTING
7839 KING 10 ACCOUNTING
7934 MILLER 10 ACCOUNTING
7566 JONES 20 RESEARCH
7902 FORD 20 RESEARCH
7876 ADAMS 20 RESEARCH
7369 SMITH 20 RESEARCH
7788 SCOTT 20 RESEARCH
7521 WARD 30 SALES
7844 TURNER 30 SALES
7499 ALLEN 30 SALES
7900 JAMES 30 SALES
7698 BLAKE 30 SALES
7654 MARTIN 30 SALES
14 rows selected
/*
但是要求把所有部门下的员工都展示出来，我们发现上面的查询是办不到的
那么，这时我们要借助右连接
*/
-- 右外连接
select e.empno,e.ename,d.deptno,d.dname
from emp e,dept d
where e.deptno(+)=d.deptno;
/* 查询结果 */
EMPNO ENAME DEPTNO DNAME
----- ---------- ------ --------------
7782 CLARK 10 ACCOUNTING
7839 KING 10 ACCOUNTING
7934 MILLER 10 ACCOUNTING
7566 JONES 20 RESEARCH
7902 FORD 20 RESEARCH
7876 ADAMS 20 RESEARCH
7369 SMITH 20 RESEARCH
7788 SCOTT 20 RESEARCH
7521 WARD 30 SALES
7844 TURNER 30 SALES
7499 ALLEN 30 SALES
7900 JAMES 30 SALES
7698 BLAKE 30 SALES
7654 MARTIN 30 SALES
40 OPERATIONS
15 rows selected
/*
e.deptno(+)=d.deptno，(+) 是oracle数据库中特有的表示方法
注意，(+) 表示外连接，
(+)在哪个表的后面表示哪个表会以null值去填充那些不满足连接条件却又在该表中的查询列，
此时应该以关键字(+)对面的表作为外连接的驱动表；
驱动表：
左外连接中驱动表是左边的表，右外连接中驱动表是右边的表。
*/
-- 左外连接
select d.deptno,d.dname,e.empno,e.ename
from emp e,dept d
where d.deptno=e.deptno(+);
/* 查询结果 */
DEPTNO DNAME EMPNO ENAME
------ -------------- ----- ----------
10 ACCOUNTING 7782 CLARK
10 ACCOUNTING 7839 KING
10 ACCOUNTING 7934 MILLER
20 RESEARCH 7566 JONES
20 RESEARCH 7902 FORD
20 RESEARCH 7876 ADAMS
20 RESEARCH 7369 SMITH
20 RESEARCH 7788 SCOTT
30 SALES 7521 WARD
30 SALES 7844 TURNER
30 SALES 7499 ALLEN
30 SALES 7900 JAMES
30 SALES 7698 BLAKE
30 SALES 7654 MARTIN
40 OPERATIONS
15 rows selected
-- 范例：查询所有员工的上级领导
select e1.empno,e1.ename,e2.empno bossno,e2.ename bossname
from emp e1,emp e2
where e1.mgr=e2.empno;
/* 查询结果 */
EMPNO ENAME BOSSNO BOSSNAME
----- ---------- ------ ----------
7902 FORD 7566 JONES
7788 SCOTT 7566 JONES
7844 TURNER 7698 BLAKE
7499 ALLEN 7698 BLAKE
7521 WARD 7698 BLAKE
7900 JAMES 7698 BLAKE
7654 MARTIN 7698 BLAKE
7934 MILLER 7782 CLARK
7876 ADAMS 7788 SCOTT
7698 BLAKE 7839 KING
7566 JONES 7839 KING
7782 CLARK 7839 KING
7369 SMITH 7902 FORD
13 rows selected
/*
分析：
通过查询结果发现KING的上级领导没有展示出来，所以这时我们要借助外连接把他查询出来
*/
-- 左外连接
select e1.empno,e1.ename,e2.empno bossno,e2.ename bossname
from emp e1,emp e2
where e1.mgr=e2.empno(+);
/* 查询结果 */
SQL>
EMPNO ENAME BOSSNO BOSSNAME
----- ---------- ------ ----------
7902 FORD 7566 JONES
7788 SCOTT 7566 JONES
7900 JAMES 7698 BLAKE
7844 TURNER 7698 BLAKE
7654 MARTIN 7698 BLAKE
7521 WARD 7698 BLAKE
7499 ALLEN 7698 BLAKE
7934 MILLER 7782 CLARK
7876 ADAMS 7788 SCOTT
7782 CLARK 7839 KING
7698 BLAKE 7839 KING
7566 JONES 7839 KING
7369 SMITH 7902 FORD
7839 KING
14 rows selected
/*
为什么要使用左连接？
因为，左边员工表里面有KING，右边boss表里面没有KING的上级，现在要连接查询，所以用左外连接
*/
/*
下面我们来看一下，查询每个员工的下级
*/
-- 使用左外连接
select e1.empno,e1.ename,e2.empno 下级no,e2.ename 下级name
from emp e1,emp e2
where e1.empno=e2.mgr(+);
/* 查询结果 */
EMPNO ENAME 下级NO 下级NAME
----- ---------- ------ ----------
7369 SMITH
7499 ALLEN
7521 WARD
7566 JONES 7902 FORD
7566 JONES 7788 SCOTT
7654 MARTIN
7698 BLAKE 7844 TURNER
7698 BLAKE 7499 ALLEN
7698 BLAKE 7521 WARD
7698 BLAKE 7900 JAMES
7698 BLAKE 7654 MARTIN
7782 CLARK 7934 MILLER
7788 SCOTT 7876 ADAMS
7839 KING 7698 BLAKE
7839 KING 7566 JONES
7839 KING 7782 CLARK
7844 TURNER
7876 ADAMS
7900 JAMES
7902 FORD 7369 SMITH
EMPNO ENAME 下级NO 下级NAME
----- ---------- ------ ----------
7934 MILLER
21 rows selected
/*
下面使用 left/right (outer) join on 语法
左连接语法：
目标表1 left (outer) join 目标表2 on (连接条件)
右连接语法：
目标表1 right (outer) join 目标表2 on (连接条件)
*/
-- 查询各个员工的上级
-- 左外连接
select e1.empno,e1.ename,e2.empno bossno,e2.ename bossname
from emp e1 left outer join emp e2 on (e1.mgr=e2.empno);
/* 查询结果 */
EMPNO ENAME BOSSNO BOSSNAME
----- ---------- ------ ----------
7902 FORD 7566 JONES
7788 SCOTT 7566 JONES
7900 JAMES 7698 BLAKE
7844 TURNER 7698 BLAKE
7654 MARTIN 7698 BLAKE
7521 WARD 7698 BLAKE
7499 ALLEN 7698 BLAKE
7934 MILLER 7782 CLARK
7876 ADAMS 7788 SCOTT
7782 CLARK 7839 KING
7698 BLAKE 7839 KING
7566 JONES 7839 KING
7369 SMITH 7902 FORD
7839 KING
14 rows selected
-- 右外连接
select e1.empno,e1.ename,e2.empno bossname,e2.ename bossname
from emp e2 right outer join emp e1 on (e1.mgr=e2.empno);
/* 查询结果 */
EMPNO ENAME BOSSNAME BOSSNAME
----- ---------- -------- ----------
7902 FORD 7566 JONES
7788 SCOTT 7566 JONES
7900 JAMES 7698 BLAKE
7844 TURNER 7698 BLAKE
7654 MARTIN 7698 BLAKE
7521 WARD 7698 BLAKE
7499 ALLEN 7698 BLAKE
7934 MILLER 7782 CLARK
7876 ADAMS 7788 SCOTT
7782 CLARK 7839 KING
7698 BLAKE 7839 KING
7566 JONES 7839 KING
7369 SMITH 7902 FORD
7839 KING
14 rows selected
-- 查询每个员工的下级
-- 左外连接
select e1.empno,e1.ename,e2.empno,e2.ename
from emp e1 left outer join emp e2 on (e1.empno=e2.mgr);
/* 查询结果 */
EMPNO ENAME EMPNO ENAME
----- ---------- ----- ----------
7369 SMITH
7499 ALLEN
7521 WARD
7566 JONES 7902 FORD
7566 JONES 7788 SCOTT
7654 MARTIN
7698 BLAKE 7844 TURNER
7698 BLAKE 7499 ALLEN
7698 BLAKE 7521 WARD
7698 BLAKE 7900 JAMES
7698 BLAKE 7654 MARTIN
7782 CLARK 7934 MILLER
7788 SCOTT 7876 ADAMS
7839 KING 7698 BLAKE
7839 KING 7566 JONES
7839 KING 7782 CLARK
7844 TURNER
7876 ADAMS
7900 JAMES
7902 FORD 7369 SMITH
EMPNO ENAME EMPNO ENAME
----- ---------- ----- ----------
7934 MILLER
21 rows selected
-- 右外连接
select e1.empno,e1.ename,e2.empno lowno,e2.ename lowname
from emp e2 right join emp e1 on (e2.mgr=e1.empno);
/* 查询结果 */
EMPNO ENAME LOWNO LOWNAME
----- ---------- ----- ----------
7369 SMITH
7499 ALLEN
7521 WARD
7566 JONES 7902 FORD
7566 JONES 7788 SCOTT
7654 MARTIN
7698 BLAKE 7844 TURNER
7698 BLAKE 7499 ALLEN
7698 BLAKE 7521 WARD
7698 BLAKE 7900 JAMES
7698 BLAKE 7654 MARTIN
7782 CLARK 7934 MILLER
7788 SCOTT 7876 ADAMS
7839 KING 7698 BLAKE
7839 KING 7566 JONES
7839 KING 7782 CLARK
7844 TURNER
7876 ADAMS
7900 JAMES
7902 FORD 7369 SMITH
EMPNO ENAME LOWNO LOWNAME
----- ---------- ----- ----------
7934 MILLER
21 rows selected
都看到最后了啦，如果觉得写得好的话呐
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