Oracle 数据库入门之----------------------多表查询

多表查询

SQL> --工资总额

SQL> select sum(sal) from emp;

  SUM(SAL)                                                                                                                                                                                              

----------                                                                                                                                                                                              

     29025                                                                                                                                                                                              

SQL> --人数

SQL> select count(*) from emp;

  COUNT(*)                                                                                                                                                                                              

----------                                                                                                                                                                                              

        14                                                                                                                                                                                              

SQL> --平均工资

SQL> select sum(sal)/count(*) 一,avg(sal) 二 from emp;

        一         二                                                                                                                                                                                   

---------- ----------                                                                                                                                                                                   

2073.21429 2073.21429                                                                                                                                                                                   

SQL> --平均奖金

SQL> select sum(comm)/count(*) 一,sum(comm)/count(comm) 二,avg(comm) 三

  2  from emp;

        一         二         三                                                                                                                                                                        

---------- ---------- ----------                                                                                                                                                                        

157.142857        550        550                                                                                                                                                                        

SQL> select count(*), count(comm) from emp;

  COUNT(*) COUNT(COMM)                                                                                                                                                                                  

---------- -----------                                                                                                                                                                                  

        14           4                                                                                                                                                                                  

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> --null值 5. 组函数会自动滤空；

SQL> select count(*), count(nvl(comm,0)) from emp;

  COUNT(*) COUNT(NVL(COMM,0))                                                                                                                                                                           

---------- ------------------                                                                                                                                                                           

        14                 14                                                                                                                                                                           

SQL> --null值 5. 组函数会自动滤空；可以嵌套滤空函数来屏蔽他的滤空功能

SQL> host cls

SQL> --每个部门的平均工资

SQL> select deptno,avg(sal)

  2  from emp

  3  group by deptno;

    DEPTNO   AVG(SAL)                                                                                                                                                                                   

---------- ----------                                                                                                                                                                                   

        30 1566.66667                                                                                                                                                                                   

        20       2175                                                                                                                                                                                   

        10 2916.66667                                                                                                                                                                                   

SQL> --多个列的分组

SQL> select deptno,job,sum(sal)

  2  from emp

  3  group by deptno,job

  4  order by 1;

    DEPTNO JOB         SUM(SAL)                                                                                                                                                                         

---------- --------- ----------                                                                                                                                                                         

        10 CLERK           1300                                                                                                                                                                         

        10 MANAGER         2450                                                                                                                                                                         

        10 PRESIDENT       5000                                                                                                                                                                         

        20 ANALYST         6000                                                                                                                                                                         

        20 CLERK           1900                                                                                                                                                                         

        20 MANAGER         2975                                                                                                                                                                         

        30 CLERK            950                                                                                                                                                                         

        30 MANAGER         2850                                                                                                                                                                         

        30 SALESMAN        5600                                                                                                                                                                         

已选择 9 行。

SQL> --多个列的分组: 先按照第一个列分组，如果相同，再第二个列分组，以此类推

SQL> --查询平均工资大于2000的部门

SQL> select deptno,avg(sal)

  2  from emp

  3  group by deptno

  4  having avg(sal) > 2000;

    DEPTNO   AVG(SAL)