多表查询

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SQL> --查询所有部门的信息和部门下的所有员工信息
SQL> select e.empno,e.ename,job,d.deptno,d.dname
  2  from emp e,dept d
  3  where e.deptno = d.deptno;

     EMPNO ENAME                JOB                    DEPTNO                  
---------- -------------------- ------------------ ----------                  
DNAME                                                                          
----------------------------                                                   
      7369 SMITH                CLERK                      20                  
RESEARCH                                                                       
                                                                               
      7499 ALLEN                SALESMAN                   30                  
SALES                                                                          
                                                                               
      7521 WARD                 SALESMAN                   30                  
SALES                                                                          
                                                                               

     EMPNO ENAME                JOB                    DEPTNO                  
---------- -------------------- ------------------ ----------                  
DNAME                                                                          
----------------------------                                                   
      7566 JONES                MANAGER                    20                  
RESEARCH                                                                       
                                                                               
      7654 MARTIN               SALESMAN                   30                  
SALES                                                                          
                                                                               
      7698 BLAKE                MANAGER                    30                  
SALES                                                                          
                                                                               

     EMPNO ENAME                JOB                    DEPTNO                  
---------- -------------------- ------------------ ----------                  
DNAME                                                                          
----------------------------                                                   
      7782 CLARK                MANAGER                    10                  
ACCOUNTING                                                                     
                                                                               
      7788 SCOTT                ANALYST                    20                  
RESEARCH                                                                       
                                                                               
      7839 KING                 PRESIDENT                  10                  
ACCOUNTING                                                                     
                                                                               

     EMPNO ENAME                JOB                    DEPTNO                  
---------- -------------------- ------------------ ----------                  
DNAME                                                                          
----------------------------                                                   
      7844 TURNER               SALESMAN                   30                  
SALES                                                                          
                                                                               
      7876 ADAMS                CLERK                      20                  
RESEARCH                                                                       
                                                                               
      7900 JAMES                CLERK                      30                  
SALES                                                                          
                                                                               

     EMPNO ENAME                JOB                    DEPTNO                  
---------- -------------------- ------------------ ----------                  
DNAME                                                                          
----------------------------                                                   
      7902 FORD                 ANALYST                    20                  
RESEARCH                                                                       
                                                                               
      7934 MILLER               CLERK                      10                  
ACCOUNTING                                                                     
                                                                               

已选择14行。

SQL> set linesize 200;
SQL> /

     EMPNO ENAME                JOB                    DEPTNO DNAME                                                                                                                                    
---------- -------------------- ------------------ ---------- ----------------------------                                                                                                             
      7369 SMITH                CLERK                      20 RESEARCH                                                                                                                                 
      7499 ALLEN                SALESMAN                   30 SALES                                                                                                                                    
      7521 WARD                 SALESMAN                   30 SALES                                                                                                                                    
      7566 JONES                MANAGER                    20 RESEARCH                                                                                                                                 
      7654 MARTIN               SALESMAN                   30 SALES                                                                                                                                    
      7698 BLAKE                MANAGER                    30 SALES                                                                                                                                    
      7782 CLARK                MANAGER                    10 ACCOUNTING                                                                                                                               
      7788 SCOTT                ANALYST                    20 RESEARCH                                                                                                                                 
      7839 KING                 PRESIDENT                  10 ACCOUNTING                                                                                                                               
      7844 TURNER               SALESMAN                   30 SALES                                                                                                                                    
      7876 ADAMS                CLERK                      20 RESEARCH                                                                                                                                 

     EMPNO ENAME                JOB                    DEPTNO DNAME                                                                                                                                    
---------- -------------------- ------------------ ---------- ----------------------------                                                                                                             
      7900 JAMES                CLERK                      30 SALES                                                                                                                                    
      7902 FORD                 ANALYST                    20 RESEARCH                                                                                                                                 
      7934 MILLER               CLERK                      10 ACCOUNTING                                                                                                                               

已选择14行。

SQL>  -- 等值连接 用等号去连接2个表，但是一定要注意连接的2个表一定要有关系
SQL> select * from tab;

TNAME                                                        TABTYPE         CLUSTERID                                                                                                                 
------------------------------------------------------------ -------------- ----------                                                                                                                 
DEPT                                                         TABLE                                                                                                                                     
EMP                                                          TABLE                                                                                                                                     
BONUS                                                        TABLE                                                                                                                                     
SALGRADE                                                     TABLE                                                                                                                                     

SQL> selectn * from salgrade;
SP2-0734: 未知的命令开头 "selectn * ..." - 忽略了剩余的行。
SQL> select * from salgrade;

     GRADE      LOSAL      HISAL                                                                                                                                                                       
---------- ---------- ----------                                                                                                                                                                       
         1        700       1200                                                                                                                                                                       
         2       1201       1400                                                                                                                                                                       
         3       1401       2000                                                                                                                                                                       
         4       2001       3000                                                                                                                                                                       
         5       3001       9999                                                                                                                                                                       

SQL>  -- 查询员工信息和员工的工资级别
SQL> select e.empno,e.sal,s.grade,s.losal,s.hisal
  2  from emp e,salgrade s
  3  where e.sal between s.losal and s.hisal;

     EMPNO        SAL      GRADE      LOSAL      HISAL                                                                                                                                                 
---------- ---------- ---------- ---------- ----------                                                                                                                                                 
      7369        800          1        700       1200                                                                                                                                                 
      7900        950          1        700       1200                                                                                                                                                 
      7876       1100          1        700       1200                                                                                                                                                 
      7521       1250          2       1201       1400                                                                                                                                                 
      7654       1250          2       1201       1400                                                                                                                                                 
      7934       1300          2       1201       1400                                                                                                                                                 
      7844       1500          3       1401       2000                                                                                                                                                 
      7499       1600          3       1401       2000                                                                                                                                                 
      7782       2450          4       2001       3000                                                                                                                                                 
      7698       2850          4       2001       3000                                                                                                                                                 
      7566       2975          4       2001       3000                                                                                                                                                 

     EMPNO        SAL      GRADE      LOSAL      HISAL                                                                                                                                                 
---------- ---------- ---------- ---------- ----------                                                                                                                                                 
      7788       3000          4       2001       3000                                                                                                                                                 
      7902       3000          4       2001       3000                                                                                                                                                 
      7839       5000          5       3001       9999                                                                                                                                                 

已选择14行。

SQL> --不等值连接
SQL> --外连接
SQL> --统计每一个部门的人数
SQL> --显示部门号  部门名称   部门人数
SQL> select e.deptno,d.dname,count(*)
  2  from emp e,dept d
  3  where e.deptno = d.deptno
  4  group by e.deptno,d.dname
  5  ；
  6  ；
  7  ；‘；’‘’
  8  ；
  9  ;
；
*
第 5 行出现错误:
ORA-00911: 无效字符

SQL> select e.deptno,d.dname,count(*)
  2  from emp e,dept d
  3  where e.deptno = d.deptno
  4  group by e.deptno,d.dname;

    DEPTNO DNAME                          COUNT(*)                                                                                                                                                     
---------- ---------------------------- ----------                                                                                                                                                     
        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> /*
SQL> 外连接:分类左外连接和右外连接
SQL> 左外连接:  where e.deptno = d.deptno 不成立的时候,无论右边是否有数据与之对应,左边的都要显示
SQL>           where e.deptno = d.depton(+)
SQL> 右外连接:  where e.deptno = d.deptno 不成立的时候,无论左边表是否有数据与之对应,右边表都会显示
SQL>           where e.deptno(+) = d.deptno;
SQL> */
SQL> select d.deptno,d.dname,count(e.empno)
  2  from emp e,dept d
  3  where e.deptno(+) = d.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> select * from dept;

    DEPTNO DNAME                        LOC                                                                                                                                                            
---------- ---------------------------- --------------------------                                                                                                                                     
        10 ACCOUNTING                   NEW YORK                                                                                                                                                       
        20 RESEARCH                     DALLAS                                                                                                                                                         
        30 SALES                        CHICAGO                                                                                                                                                        
        40 OPERATIONS                   BOSTON                                                                                                                                                         

SQL>  -- 左外连接以左边表为主表，主表会显示所有，另一个表如果没有显示空,右外连接以右边表为主表.....
SQL> -- 内连接
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 19-4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 23-5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 领导名字,e.empno 领导ID,p.ename 员工名字,p.empno 员工ID
  2  from emp e,emp p
  3  where e.empno = p.mgr;

领导名字                 领导ID 员工名字                 员工ID                                                                                                                                        
-------------------- ---------- -------------------- ----------                                                                                                                                        
FORD                       7902 SMITH                      7369                                                                                                                                        
BLAKE                      7698 ALLEN                      7499                                                                                                                                        
BLAKE                      7698 WARD                       7521                                                                                                                                        
KING                       7839 JONES                      7566                                                                                                                                        
BLAKE                      7698 MARTIN                     7654                                                                                                                                        
KING                       7839 BLAKE                      7698                                                                                                                                        
KING                       7839 CLARK                      7782                                                                                                                                        
JONES                      7566 SCOTT                      7788                                                                                                                                        
BLAKE                      7698 TURNER                     7844                                                                                                                                        
SCOTT                      7788 ADAMS                      7876                                                                                                                                        
BLAKE                      7698 JAMES                      7900                                                                                                                                        

领导名字                 领导ID 员工名字                 员工ID                                                                                                                                        
-------------------- ---------- -------------------- ----------                                                                                                                                        
JONES                      7566 FORD                       7902                                                                                                                                        
CLARK                      7782 MILLER                     7934                                                                                                                                        

已选择13行。

SQL> select count(*) from emp e,emp p
  2  where e.empno = p.mgr;

  COUNT(*)                                                                                                                                                                                             
----------                                                                                                                                                                                             
        13                                                                                                                                                                                             

SQL> select count(*) from emp e,emp p;

  COUNT(*)                                                                                                                                                                                             
----------                                                                                                                                                                                             
       196                                                                                                                                                                                             

SQL> -- 内连接只能做数据量小的表,对于大表层次查询
SQL> -- 层次查询
SQL> select e.ename 领导名字,e.empno 领导ID
  2   from emp e
  3  connect by prior empno = mgr
  4  start with mgr is null;

领导名字                 领导ID                                                                                                                                                                        
-------------------- ----------                                                                                                                                                                        
KING                       7839                                                                                                                                                                        
JONES                      7566                                                                                                                                                                        
SCOTT                      7788                                                                                                                                                                        
ADAMS                      7876                                                                                                                                                                        
FORD                       7902                                                                                                                                                                        
SMITH                      7369                                                                                                                                                                        
BLAKE                      7698                                                                                                                                                                        
ALLEN                      7499                                                                                                                                                                        
WARD                       7521                                                                                                                                                                        
MARTIN                     7654                                                                                                                                                                        
TURNER                     7844                                                                                                                                                                        

领导名字                 领导ID                                                                                                                                                                        
-------------------- ----------                                                                                                                                                                        
JAMES                      7900                                                                                                                                                                        
CLARK                      7782                                                                                                                                                                        
MILLER                     7934                                                                                                                                                                        

已选择14行。

SQL> spool off;

多表查询

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原文地址：http://www.cnblogs.com/877599949yan/p/5286019.html