以emp 为例
奖金(comm)小于500或为空的数据
不能使用or，uion，union all,case when
------解决方案--------------------
- SQL code
SQL> select * from emp where nvl(comm,0)<500; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO FLAG----- ---------- --------- ----- ----------- --------- --------- ------ ---- 7369 SMIT H1 CLERK 7912 1980-12-17 800.00 20 7499 ALLE N SALESMAN 7698 1981-2-20 1600.00 300.00 30 7566 JONE S MANAGER 7839 1981-4-2 2975.00 20 7698 BLAK E MANAGER 7839 1981-5-1 2850.00 30 7782 CLAR K MANAGER 7839 1981-6-9 2450.00 10 7788 SCOT T ANALYST 7566 1987-4-19 3000.00 20 7839 KING PRESIDENT 1981-11-17 5000.00 10 7844 TURN ER SALESMAN 7698 1981-9-8 1500.00 0.00 30 7876 ADAM S CLERK 7788 1987-5-23 1100.00 20 7900 JAME S CLERK 7698 1981-12-3 950.00 30 7902 FORD ANALYST 7566 1981-12-3 3000.00 20 7934 MILL ER CLERK 7782 1982-1-23 1300.00 10 12 rows selected SQL>