Orcale查询练习

SQL> conn system 
已连接。 
SQL> conn scott/scott 
已连接。 
 
1.查询员工表所有数据，并说明使用*的缺点  
 
SQL> select * from emp 
  2  / 
 
     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                                                                       
                                                                                 
 
     EMPNO ENAME      JOB              MGR HIREDATE              SAL       COMM  
---------- ---------- --------- ---------- -------------- ---------- ----------   
    DEPTNO                                                                       
----------                                                                        
      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                                                                       
                                                                                 
 
     EMPNO ENAME      JOB              MGR HIREDATE              SAL       COMM  
---------- ---------- --------- ---------- -------------- ---------- ----------   
    DEPTNO                                                                       
----------                                                                        
      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                                                                       
                                                                                 
 
     EMPNO ENAME      JOB              MGR HIREDATE              SAL       COMM  
---------- ---------- --------- ---------- -------------- ---------- ----------   
    DEPTNO                                                                       
----------                                                                        
      7844 TURNER     SALESMAN        7698 08-9月 -81           1500          0  
        30                                                                       
                                                                                 
      7876 ADAMS      CLERK           7788 23-5月 -87           1100             
        20                                                                       
                                                                                 
      7900 JAMES      CLERK           7698 03-12月-81            950             
        30                                                                       
                                                                                 
 
     EMPNO ENAME      JOB              MGR HIREDATE              SAL       COMM  
---------- ---------- --------- ---------- -------------- ---------- ----------   
    DEPTNO                                                                       
----------                                                                        
      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> col sal for 9999 
SQL> col comm for 9999 
SQL> col comm for 9999; 
SQL> / 
 
EMPNO ENAME      JOB              MGR HIREDATE         SAL  COMM     DEPTNO      
----- ---------- --------- ---------- -------------- ----- ----- ----------       
 #### SMITH      CLERK           7902 17-12月-80       800               20      
 #### ALLEN      SALESMAN        7698 20-2月 -81      1600   300         30      
 #### WARD       SALESMAN        7698 22-2月 -81      1250   500         30      
 #### JONES      MANAGER         7839 02-4月 -81      2975               20      
 #### MARTIN     SALESMAN        7698 28-9月 -81      1250  1400         30      
 #### BLAKE      MANAGER         7839 01-5月 -81      2850               30      
 #### CLARK      MANAGER         7839 09-6月 -81      2450               10      
 #### SCOTT      ANALYST         7566 19-4月 -87      3000               20      
 #### KING       PRESIDENT            17-11月-81      5000               10      
 #### TURNER     SALESMAN        7698 08-9月 -81      1500     0         30      
 #### ADAMS      CLERK           7788 23-5月 -87      1100               20      
 
EMPNO ENAME      JOB              MGR HIREDATE         SAL  COMM     DEPTNO      
----- ---------- --------- ---------- -------------- ----- ----- ----------       
 #### JAMES      CLERK           7698 03-12月-81       950               30      
 #### FORD       ANALYST         7566 03-12月-81      3000               20      
 #### MILLER     CLERK           7782 23-1月 -82      1300               10      
 
已选择14行。 
 
2.查询职（job）为'PRESIDENT'的员工的工资 
 
SQL> select sal from emp where job='PRESIDENT' 
  2  / 
 
  SAL                                                                            
-----                                                                             
 5000                                                                            
 
3.查询佣金为0或为null的员工的信息 
 
SQL> select * from emp where comm is null 
  2   
SQL> / 
 
EMPNO ENAME      JOB              MGR HIREDATE         SAL  COMM     DEPTNO      
----- ---------- --------- ---------- -------------- ----- ----- ----------       
 #### SMITH      CLERK           7902 17-12月-80       800               20      
 #### JONES      MANAGER         7839 02-4月 -81      2975               20      
 #### BLAKE      MANAGER         7839 01-5月 -81      2850               30      
 #### CLARK      MANAGER         7839 09-6月 -81      2450               10      
 #### SCOTT      ANALYST         7566 19-4月 -87      3000               20      
 #### KING       PRESIDENT            17-11月-81      5000               10      
 #### ADAMS      CLERK           7788 23-5月 -87      1100               20      
 #### JAMES      CLERK           7698 03-12月-81       950               30      
 #### FORD       ANALYST         7566 03-12月-81      3000               20      
 #### MILLER     CLERK           7782 23-1月 -82      1300               10      
 
已选择10行。