oracle数据库自连接（scott表练习）

1 oracle中scott用户下的四张表

/*  表说明：    dept      --部门表    emp       --员工表    salgrade  --工资等级表    bonus     --工资表（现在不用)*/CREATE TABLE DEPT (  DEPTNO NUMBER(2) CONSTRAINT PK_DEPT PRIMARY KEY,     DNAME VARCHAR2(15),    LOC VARCHAR2(60) );CREATE TABLE EMP (  EMPNO NUMBER(4) CONSTRAINT PK_EMP PRIMARY KEY,    ENAME VARCHAR2(15),    JOB VARCHAR2(9),    MGR NUMBER(4),    HIREDATE DATE,    SAL NUMBER(7,2),    COMM NUMBER(7,2),    DEPTNO NUMBER(2) CONSTRAINT FK_DEPTNO REFERENCES DEPT);CREATE TABLE SALGRADE (   GRADE NUMBER,    LOSAL NUMBER,    HISAL NUMBER );CREATE TABLE BONUS (    ENAME VARCHAR2(15),    JOB VARCHAR2(9),    SAL NUMBER,    COMM NUMBER);-- 查看已有表select table_name,tablespace_name,status,temporary,table_lock from user_tables;-- 插入数据-- 先插入主表DEPT数据INSERT INTO DEPT VALUES (10,'ACCOUNTING','NEW YORK');INSERT INTO DEPT VALUES (20,'RESEARCH','DALLAS');INSERT INTO DEPT VALUES (30,'SALES','CHICAGO');INSERT INTO DEPT VALUES (40,'OPERATIONS','BOSTON');-- 插入员工表EMP数据INSERT INTO EMP VALUES(7369,'SMITH','CLERK',7902,to_date('17-12-1980','dd-mm-yyyy'),800,NULL,20);INSERT INTO EMP VALUES(7499,'ALLEN','SALESMAN',7698,to_date('20-2-1981','dd-mm-yyyy'),1600,300,30);INSERT INTO EMP VALUES(7521,'WARD','SALESMAN',7698,to_date('22-2-1981','dd-mm-yyyy'),1250,500,30);INSERT INTO EMP VALUES(7566,'JONES','MANAGER',7839,to_date('2-4-1981','dd-mm-yyyy'),2975,NULL,20);INSERT INTO EMP VALUES(7654,'MARTIN','SALESMAN',7698,to_date('28-9-1981','dd-mm-yyyy'),1250,1400,30);INSERT INTO EMP VALUES(7698,'BLAKE','MANAGER',7839,to_date('1-5-1981','dd-mm-yyyy'),2850,NULL,30);INSERT INTO EMP VALUES(7782,'CLARK','MANAGER',7839,to_date('9-6-1981','dd-mm-yyyy'),2450,NULL,10);INSERT INTO EMP VALUES(7788,'SCOTT','ANALYST',7566,to_date('13-7-87','dd-mm-rr')-85,3000,NULL,20);INSERT INTO EMP VALUES(7839,'KING','PRESIDENT',NULL,to_date('17-11-1981','dd-mm-yyyy'),5000,NULL,10);INSERT INTO EMP VALUES(7844,'TURNER','SALESMAN',7698,to_date('8-9-1981','dd-mm-yyyy'),1500,0,30);INSERT INTO EMP VALUES(7876,'ADAMS','CLERK',7788,to_date('13-7-87', 'dd-mm-rr')-51,1100,NULL,20);INSERT INTO EMP VALUES(7900,'JAMES','CLERK',7698,to_date('3-12-1981','dd-mm-yyyy'),950,NULL,30);INSERT INTO EMP VALUES(7902,'FORD','ANALYST',7566,to_date('3-12-1981','dd-mm-yyyy'),3000,NULL,20);INSERT INTO EMP VALUES(7934,'MILLER','CLERK',7782,to_date('23-1-1982','dd-mm-yyyy'),1300,NULL,10);-- 插入薪资等级表SALGRADE数据INSERT INTO SALGRADE VALUES (1,700,1200);INSERT INTO SALGRADE VALUES (2,1201,1400);INSERT INTO SALGRADE VALUES (3,1401,2000);INSERT INTO SALGRADE VALUES (4,2001,3000);INSERT INTO SALGRADE VALUES (5,3001,9999);-- 统一提交commit;

2 表之间关系图

3 查询语句练习

3.1 自连接查询

自连结其实就是一个等值连接。

比如：查询出员工及他的上级。

理解：scott这个表中，员工中包含管理者，即员工大于管理者，也可以说管理者也是一个员工。这样的话，就可以通过自连接的方式找到员工的上级，也可以通过这种方式，找到一个领导的下级。

下面这个示例是通过员工的编号可以找到他的上级的编号。

-- 自连接(empno员工，mgr管理者。注意：管理者也属于员工)select e1.empno, e1.ename , e1.mgr ,e2.empno,e2.ename from emp e1 ,emp e2where e1.mgr = e2 .empno ;-- 测试select * from emp where empno = 7902 ;