要显示雇员名,雇员工资及所在部门的名字
第一步:select * from emp a1,dept a2
没有连接条件的返回结果会形成笛卡尔积,结果如下。很多生成的记录是没有意义的。
EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO | DETPNO | DNAME | LOC | |
1 | 7369 | SMITH | CLERK | 7902 | 1980/12/17 | 800 | 20 | 10 | ACCOUNTING | NEW YORK | |
2 | 7499 | ALLEN | SALESMAN | 7698 | 1981/2/20 | 1600 | 300 | 30 | 10 | ACCOUNTING | NEW YORK |
3 | 7521 | WARD | SALESMAN | 7698 | 1981/2/22 | 1250 | 500 | 30 | 10 | ACCOUNTING | NEW YORK |
4 | 7566 | JONES | MANAGER | 7839 | 1981/4/2 | 2975 | 20 | 10 | ACCOUNTING | NEW YORK | |
5 | 7654 | MARTIN | SALESMAN | 7698 | 1981/9/28 | 1250 | 1400 | 30 | 10 | ACCOUNTING | NEW YORK |
6 | 7698 | BLAKE | MANAGER | 7839 | 1981/5/1 | 2850 | 30 | 10 | ACCOUNTING | NEW YORK | |
7 | 7782 | CLARK | MANAGER | 7839 | 1981/6/9 | 2450 | 10 | 10 | ACCOUNTING | NEW YORK | |
8 | 7788 | SCOTT | ANALYST | 7566 | 1987/4/19 | 1500 | 20 | 10 | ACCOUNTING | NEW YORK | |
9 | 7839 | KING | PRESIDENT | 1981/11/17 | 5000 | 10 | 10 | ACCOUNTING | NEW YORK | ||
10 | 7844 | TURNER | SALESMAN | 7698 | 1981/9/8 | 1500 | 0 | 30 | 10 | ACCOUNTING | NEW YORK |
11 | 7876 | ADAMS | CLERK | 7788 | 1987/5/23 | 1100 | 20 | 10 | ACCOUNTING | NEW YORK | |
12 | 7900 | JAMES | CLERK | 7698 | 1981/12/3 | 950 | 30 | 10 | ACCOUNTING | NEW YORK | |
13 | 7902 | FORD | ANALYST | 7566 | 1981/12/3 | 3000 | 20 | 10 | ACCOUNTING | NEW YORK | |
14 | 7934 | MILLER | CLERK | 7782 | 1982/1/23 | 1300 | 10 | 10 | ACCOUNTING | NEW YORK | |
15 | 7369 | SMITH | CLERK | 7902 | 1980/12/17 | 800 | 20 | 20 | RESEARCH | DALLAS | |
16 | 7499 | ALLEN | SALESMAN | 7698 | 1981/2/20 | 1600 | 300 | 30 | 20 | RESEARCH | DALLAS |
17 | 7521 | WARD | SALESMAN | 7698 | 1981/2/22 | 1250 | 500 | 30 | 20 | RESEARCH | DALLAS |
18 | 7566 | JONES | MANAGER | 7839 | 1981/4/2 | 2975 | 20 | 20 | RESEARCH | DALLAS | |
19 | 7654 | MARTIN | SALESMAN | 7698 | 1981/9/28 | 1250 | 1400 | 30 | 20 | RESEARCH | DALLAS |
20 | 7698 | BLAKE | MANAGER | 7839 | 1981/5/1 | 2850 | 30 | 20 | RESEARCH | DALLAS | |
21 | 7782 | CLARK | MANAGER | 7839 | 1981/6/9 | 2450 | 10 | 20 | RESEARCH | DALLAS | |
22 | 7788 | SCOTT | ANALYST | 7566 | 1987/4/19 | 1500 | 20 | 20 | RESEARCH | DALLAS | |
23 | 7839 | KING | PRESIDENT | 1981/11/17 | 5000 | 10 | 20 | RESEARCH | DALLAS | ||
24 | 7844 | TURNER | SALESMAN | 7698 | 1981/9/8 | 1500 | 0 | 30 | 20 | RESEARCH | DALLAS |
25 | 7876 | ADAMS | CLERK | 7788 | 1987/5/23 | 1100 | 20 | 20 | RESEARCH | DALLAS | |
26 | 7900 | JAMES | CLERK | 7698 | 1981/12/3 | 950 | 30 | 20 | RESEARCH | DALLAS | |
27 | 7902 | FORD | ANALYST | 7566 | 1981/12/3 | 3000 | 20 | 20 | RESEARCH | DALLAS | |
28 | 7934 | MILLER | CLERK | 7782 | 1982/1/23 | 1300 | 10 | 20 | RESEARCH | DALLAS | |
29 | 7369 | SMITH | CLERK | 7902 | 1980/12/17 | 800 | 20 | 30 | SALES | CHICAGO | |
30 | 7499 | ALLEN | SALESMAN | 7698 | 1981/2/20 | 1600 | 300 | 30 | 30 | SALES | CHICAGO |
31 | 7521 | WARD | SALESMAN | 7698 | 1981/2/22 | 1250 | 500 | 30 | 30 | SALES | CHICAGO |
32 | 7566 | JONES | MANAGER | 7839 | 1981/4/2 | 2975 | 20 | 30 | SALES | CHICAGO | |
33 | 7654 | MARTIN | SALESMAN | 7698 | 1981/9/28 | 1250 | 1400 | 30 | 30 | SALES | CHICAGO |
34 | 7698 | BLAKE | MANAGER | 7839 | 1981/5/1 | 2850 | 30 | 30 | SALES | CHICAGO | |
35 | 7782 | CLARK | MANAGER | 7839 | 1981/6/9 | 2450 | 10 | 30 | SALES | CHICAGO | |
36 | 7788 | SCOTT | ANALYST | 7566 | 1987/4/19 | 1500 | 20 | 30 | SALES | CHICAGO | |
37 | 7839 | KING | PRESIDENT | 1981/11/17 | 5000 | 10 | 30 | SALES | CHICAGO | ||
38 | 7844 | TURNER | SALESMAN | 7698 | 1981/9/8 | 1500 | 0 | 30 | 30 | SALES | CHICAGO |
39 | 7876 | ADAMS | CLERK | 7788 | 1987/5/23 | 1100 | 20 | 30 | SALES | CHICAGO | |
40 | 7900 | JAMES | CLERK | 7698 | 1981/12/3 | 950 | 30 | 30 | SALES | CHICAGO | |
41 | 7902 | FORD | ANALYST | 7566 | 1981/12/3 | 3000 | 20 | 30 | SALES | CHICAGO | |
42 | 7934 | MILLER | CLERK | 7782 | 1982/1/23 | 1300 | 10 | 30 | SALES | CHICAGO | |
43 | 7369 | SMITH | CLERK | 7902 | 1980/12/17 | 800 | 20 | 40 | OPERATIONS | BOSTON | |
44 | 7499 | ALLEN | SALESMAN | 7698 | 1981/2/20 | 1600 | 300 | 30 | 40 | OPERATIONS | BOSTON |
45 | 7521 | WARD | SALESMAN | 7698 | 1981/2/22 | 1250 | 500 | 30 | 40 | OPERATIONS | BOSTON |
46 | 7566 | JONES | MANAGER | 7839 | 1981/4/2 | 2975 | 20 | 40 | OPERATIONS | BOSTON | |
47 | 7654 | MARTIN | SALESMAN | 7698 | 1981/9/28 | 1250 | 1400 | 30 | 40 | OPERATIONS | BOSTON |
48 | 7698 | BLAKE | MANAGER | 7839 | 1981/5/1 | 2850 | 30 | 40 | OPERATIONS | BOSTON | |
49 | 7782 | CLARK | MANAGER | 7839 | 1981/6/9 | 2450 | 10 | 40 | OPERATIONS | BOSTON | |
50 | 7788 | SCOTT | ANALYST | 7566 | 1987/4/19 | 1500 | 20 | 40 | OPERATIONS | BOSTON | |
51 | 7839 | KING | PRESIDENT | 1981/11/17 | 5000 | 10 | 40 | OPERATIONS | BOSTON | ||
52 | 7844 | TURNER | SALESMAN | 7698 | 1981/9/8 | 1500 | 0 | 30 | 40 | OPERATIONS | BOSTON |
53 | 7876 | ADAMS | CLERK | 7788 | 1987/5/23 | 1100 | 20 | 40 | OPERATIONS | BOSTON | |
54 | 7900 | JAMES | CLERK | 7698 | 1981/12/3 | 950 | 30 | 40 | OPERATIONS | BOSTON | |
55 | 7902 | FORD | ANALYST | 7566 | 1981/12/3 | 3000 | 20 | 40 | OPERATIONS | BOSTON | |
56 | 7934 | MILLER | CLERK | 7782 | 1982/1/23 | 1300 | 10 | 40 | OPERATIONS | BOSTON |
第二步,等值连接消除笛卡尔积
select * from emp a1,dept a2 where a1.deptno=a2.deptno;
第三步,选取列
select a1.ename,a1.sal,a2.dname from emp a1,dept a2 where a1.deptno=a2.deptno;