LNNVL

SELECT E.LAST_NAME,E.COMMISSION_PCT FROM EMPLOYEES E WHERE E.COMMISSION_PCT<=0.15 OR  E.COMMISSION_PCT IS NULL;
等价于
SELECT E.LAST_NAME,E.COMMISSION_PCT FROM EMPLOYEES E WHERE LNNVL(E.COMMISSION_PCT>0.15);

 

该函数不能用于复合条件如AND, OR,  BETWEEN中

可避免遗漏NULL值