以emp,dept表为例说明 SQL> select * from emp; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ---------- ---------- --------- ---------- --------- ---------- ---------- ---------- 7369 SMITH CLERK 7902 17-DEC-80 800 20 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 7566 JONES MANAGER 7839 02-APR-81 2975 20 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 7782 CLARK MANAGER 7839 09-JUN-81 2450 10 7788 SCOTT ANALYST 7566 19-APR-87 3000 20 7839 KING PRESIDENT 17-NOV-81 5000 10 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 7876 ADAMS CLERK 7788 23-MAY-87 1100 20 7900 JAMES CLERK 7698 03-DEC-81 950 30 7902 FORD ANALYST 7566 03-DEC-81 3000 20 7934 MILLER CLERK 7782 23-JAN-82 1300 10 1234 dfff aaa 7369 06-JUN-18 1600 100 10 15 rows selected. SQL> select * from dept; DEPTNO DNAME LOC ---------- -------------- ------------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON
1.内连接 inner join/join
与select 多表查询的结果一样
#列出所有“CLERK”(办事员)的姓名及其部门名称。 #多表查询 select e.ename,d.dname from dept d,emp e where d.deptno=e.deptno and e.job='CLERK'; #内连接 select e.ename,d.dname from emp e join dept d on (e.deptno=d.deptno) where e.job='CLERK'; #()可不写 ENAME DNAME ---------- -------------- MILLER ACCOUNTING SMITH RESEARCH ADAMS RESEARCH JAMES SALES
2.左外连接 left join/left outer join
显示左表的全部数据和左表右表匹配后的数据
select * from t_A a left join t_B b on a.id=b.id; t_A 看做左表 t_B 看做右表即匹配表 结果集是t_A的所有数据，t_A与t_B匹配后的数据，t_B记录不足的地方为null 或者 select * from t_A a,t_B b where a.id=b.id(+) #b为匹配表 "+" 表示补充，哪个表有“+” 哪个表就是匹配表举一个栗子
#列出部门名称和这些部门的员工信息，同时列出没有员工的部门 select d.dname,e.* from dept d left join emp e on d.deptno=e.deptno; 或者 select d.dname,e.* from dept d,emp e where d.deptno=e.deptno(+); DNAME EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO -------------- ---------- ---------- --------- ---------- --------- ---------- ---------- ---------- ACCOUNTING 7782 CLARK MANAGER 7839 09-JUN-81 2450 10 ACCOUNTING 1234 dfff aaa 7369 06-JUN-18 1600 100 10 ACCOUNTING 7839 KING PRESIDENT 17-NOV-81 5000 10 ACCOUNTING 7934 MILLER CLERK 7782 23-JAN-82 1300 10 RESEARCH 7566 JONES MANAGER 7839 02-APR-81 2975 20 RESEARCH 7369 SMITH CLERK 7902 17-DEC-80 800 20 RESEARCH 7788 SCOTT ANALYST 7566 19-APR-87 3000 20 RESEARCH 7902 FORD ANALYST 7566 03-DEC-81 3000 20 RESEARCH 7876 ADAMS CLERK 7788 23-MAY-87 1100 20 SALES 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 SALES 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 SALES 7900 JAMES CLERK 7698 03-DEC-81 950 30 SALES 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 SALES 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 SALES 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 OPERATIONS3.右外连接 right join/rignt outer join
以右表为基础，显示右表的所有记录，以及左表与右表的匹配记录
支持“+”
4.全外连接 full join/full outer join
左右表不作限制，所有的记录都显示，不支持“+”
5.自连接 self join
#查看员工名及其上级的名字
select a.ename as leader,b.ename from emp a,emp b where a.empno=b.mgr;
LEADER ENAME
---------- ----------
SMITH dfff
JONES FORD
JONES SCOTT
BLAKE ALLEN
BLAKE WARD
BLAKE JAMES