一般来说，问题能重现就是好消息，最怕不能重现。
SQL> connscott/tiger;
Connected.
SQL> descemp
Name Null? Type
------------------------------------------------- -----------------
EMPNO NOT NULLNUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NUMBER(2)
SQL> createtable emp1 as select * from emp;
Table created.
SQL> insertinto emp(empno,ename) values(8888,'Dave');
1 row created.
SQL>commit;
Commitcomplete.
SQL> selectempno,ename from emp where job not in (select job from emp1);
no rowsselected
SQL> selectempno,ename from emp where job in(select job from emp1);
EMPNO ENAME
--------------------
7934 MILLER
7900 JAMES
7876 ADAMS
7369 SMITH
7844 TURNER
7654 MARTIN
7521 WARD
7499 ALLEN
7782 CLARK
7698 BLAKE
7566 JONES
EMPNO ENAME
--------------------
7902 FORD
7788 SCOTT
7839 KING
14 rowsselected.
SQL>select empno,ename from emp A where not exists ( SELECT * FROM emp1 Bwhere B.job = A.job);
EMPNO ENAME
--------------------
8888 Dave
SQL>select empno,ename from emp A where exists ( SELECT * FROM emp1 B where B.job = A.job);
EMPNO ENAME
--------------------
7934 MILLER
7900 JAMES
7876 ADAMS
7369 SMITH
7844 TURNER
7654 MARTIN
7521 WARD
7499 ALLEN
7782 CLARK
7698 BLAKE
7566 JONES
EMPNO ENAME
--------------------
7902 FORD
7788 SCOTT
7839 KING
14 rowsselected.