.emp表数据如下
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
7369 SMITH CLERK 7902 1980/12/17 800.00 　 20
7499 ALLEN SALESMAN 7698 1981/2/20 1600.00 0.00 30
下面代码输出的结果是：（）
……
ResultSet rs = stmt.executeQuery ("select comm from emp");
while(rs.next()) {
System.out.println(rs.getDouble(1) + "," +rs.wasNull());
}
A.0, true 0, false
B.null, true 0,false
C.0, false 0, false
D.0, true 0, true
答案为啥是A 而不是B