NVL，NVL2

1、NVL(expr1,expr2)

expr1为空时则返回值为expr2的值，

SELECT last_name,

       salary,

       commission_pct,

       NVL2(commission_pct, salary + (salary * commission_pct), salary) income

  FROM employees

 WHERE last_name like 'B%'

 ORDER BY last_name;



2、NVL2(expr1,expr2,expr3)

expr1值为空时，返回expr3的值，不为空时返回expr2的值

SELECT last_name,

       salary,

       commission_pct,

       NVL(commission_pct,0.5) commission_pct2

  FROM employees

 WHERE last_name like 'B%'

 ORDER BY last_name;