oracle多表查询（外连接，自连接）

SQL> host cls

SQL> –等值连接

SQL> –查询员工信息： 员工号 姓名 月薪 部门名称

SQL> desc dept

名称 是否为空? 类型

DEPTNO NOT NULL NUMBER(2)

DNAME VARCHAR2(14)

LOC VARCHAR2(13)

SQL> select empno,ename,sal,dname

2 from emp,dept

3 where emp.deptno=dept.deptno;

EMPNO ENAME        SAL DNAME

7369 SMITH        800 RESEARCH
7499 ALLEN       1600 SALES
7521 WARD        1250 SALES
7566 JONES       2975 RESEARCH
7654 MARTIN      1250 SALES
7698 BLAKE       2850 SALES
7782 CLARK       2450 ACCOUNTING
7788 SCOTT       3000 RESEARCH
7839 KING        5000 ACCOUNTING
7844 TURNER      1500 SALES
7876 ADAMS       1100 RESEARCH

EMPNO ENAME        SAL DNAME

7900 JAMES        950 SALES
7902 FORD        3000 RESEARCH
7934 MILLER      1300 ACCOUNTING

已选择14行。

SQL> ed

已写入 file afiedt.buf

1 select empno,ename,sal,dname

2 from emp e,dept d

3* where e.deptno=d.deptno

SQL> /

EMPNO ENAME        SAL DNAME

7369 SMITH        800 RESEARCH
7499 ALLEN       1600 SALES
7521 WARD        1250 SALES
7566 JONES       2975 RESEARCH
7654 MARTIN      1250 SALES
7698 BLAKE       2850 SALES
7782 CLARK       2450 ACCOUNTING
7788 SCOTT       3000 RESEARCH
7839 KING        5000 ACCOUNTING
7844 TURNER      1500 SALES
7876 ADAMS       1100 RESEARCH

EMPNO ENAME        SAL DNAME

7900 JAMES        950 SALES
7902 FORD        3000 RESEARCH
7934 MILLER      1300 ACCOUNTING

已选择14行。

SQL> host cls

SQL> –不等值连接

SQL> –查询员工信息: 姓名 月薪 工资级别

SQL> select * from tab;

TNAME TABTYPE CLUSTERID

DEPT TABLE

EMP TABLE

BONUS TABLE

SALGRADE TABLE

SQL> select * from salgrade;

GRADE      LOSAL      HISAL

1        700       1200
2       1201       1400
3       1401       2000
4       2001       3000
5       3001       9999

SQL> select ename,sal,grade

2 from emp e,salgrade s

3 where e.sal between s.losal and s.hisal;

ENAME SAL GRADE

SMITH 800 1

JAMES 950 1

ADAMS 1100 1

WARD 1250 2

MARTIN 1250 2

MILLER 1300 2

TURNER 1500 3

ALLEN 1600 3

CLARK 2450 4

BLAKE 2850 4

JONES 2975 4

ENAME SAL GRADE

SCOTT 3000 4

FORD 3000 4

KING 5000 5

已选择14行。

SQL> host cls

SQL> –外连接

SQL> –按部门统计员工人数： 部门号 部门名称 人数

SQL> select d.deptno,d.dname,count(e.empno)

2 from dept d,emp e

3 where d.deptno=e.deptno

4 group by d.deptno,d.dname;

DEPTNO DNAME          COUNT(E.EMPNO)

10 ACCOUNTING                  3
20 RESEARCH                    5
30 SALES                       6

SQL> select * from dept;

DEPTNO DNAME          LOC

10 ACCOUNTING     NEW YORK
20 RESEARCH       DALLAS
30 SALES          CHICAGO
40 OPERATIONS     BOSTON

SQL> select * from emp where deptno=40;

未选定行

SQL> /*

SQL> 外连接解决的问题：当条件不成立时，任然希望在结果中包含不成立的记录

SQL> 左外连接: where d.deptno=e.deptno 当不成立时，等号左边代表的表的信息任然被包含

SQL> 写法: where d.deptno=e.deptno(+)

SQL> 右外连接: where d.deptno=e.deptno 当不成立时，等号右边代表的表的信息任然被包含

SQL> 写法：where d.deptno(+)=e.deptno

SQL> */

SQL> select d.deptno,d.dname,count(e.empno)

2 from dept d,emp e

3 where d.deptno=e.deptno(+)

4 group by d.deptno,d.dname;

DEPTNO DNAME          COUNT(E.EMPNO)

10 ACCOUNTING                  3
40 OPERATIONS                  0
20 RESEARCH                    5
30 SALES                       6

SQL> ed

已写入 file afiedt.buf

1 select d.deptno,d.dname,count(e.empno)

2 from dept d,emp e

3 where d.deptno=e.deptno(+)

4 group by d.deptno,d.dname

5* order by 1

SQL> /

DEPTNO DNAME          COUNT(E.EMPNO)

10 ACCOUNTING                  3
20 RESEARCH                    5
30 SALES                       640 OPERATIONS                  0

SQL> host cls

SQL> –自连接

SQL> –查询员工信息：的老板是

SQL> select * from emp;

EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO

7369 SMITH      CLERK           7902 17-12月-80       800                    20
7499 ALLEN      SALESMAN        7698 20-2月 -81      1600        300         30
7521 WARD       SALESMAN        7698 22-2月 -81      1250        500         30
7566 JONES      MANAGER         7839 02-4月 -81      2975                    20
7654 MARTIN     SALESMAN        7698 28-9月 -81      1250       1400         30
7698 BLAKE      MANAGER         7839 01-5月 -81      2850                    30
7782 CLARK      MANAGER         7839 09-6月 -81      2450                    10
7788 SCOTT      ANALYST         7566 13-7月 -87      3000                    20
7839 KING       PRESIDENT            17-11月-81      5000                    10
7844 TURNER     SALESMAN        7698 08-9月 -81      1500          0         30
7876 ADAMS      CLERK           7788 13-7月 -87      1100                    20

EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO

7900 JAMES      CLERK           7698 03-12月-81       950                    30
7902 FORD       ANALYST         7566 03-12月-81      3000                    20
7934 MILLER     CLERK           7782 23-1月 -82      1300                    10

已选择14行。

SQL> select e.ename||’的老板是’||b.ename

2 from emp e,emp b

3 where e.mgr=b.empno;

E.ENAME||’的老板是’||B.ENAME

FORD的老板是JONES

SCOTT的老板是JONES

JAMES的老板是BLAKE

TURNER的老板是BLAKE

MARTIN的老板是BLAKE

WARD的老板是BLAKE

ALLEN的老板是BLAKE

MILLER的老板是CLARK

ADAMS的老板是SCOTT

CLARK的老板是KING

BLAKE的老板是KING

E.ENAME||’的老板是’||B.ENAME

JONES的老板是KING

SMITH的老板是FORD

已选择13行。

SQL> –自连接：利用表的别名，将同一张表视为多张表

SQL> –层次查询

SQL> –自连接不太适合操作大表

SQL>

SQL>

SQL>

SQL> –层次查询: 对同一张表的前后两次操作，进行连接

SQL> select level,empno,ename,mgr

2 from emp

3 connect by prior empno=mgr

4 start with mgr is null

5 order by 1;

LEVEL      EMPNO ENAME             MGR

1       7839 KING
2       7566 JONES            7839
2       7698 BLAKE            7839
2       7782 CLARK            7839
3       7902 FORD             7566
3       7521 WARD             7698
3       7900 JAMES            7698
3       7934 MILLER           7782
3       7499 ALLEN            7698
3       7788 SCOTT            7566
3       7654 MARTIN           7698

LEVEL      EMPNO ENAME             MGR

3       7844 TURNER           7698
4       7876 ADAMS            7788
4       7369 SMITH            7902

已选择14行。

SQL> spool off