编写QUERY中客户出口变量时需选择I_STEP数值，I_STEP的作用是标识了该调用变量发生的时机，常用的为‘1’、‘2’,解释如下：
1） I_STEP = 1: Call is made directly before variable entry.
2） I_STEP = 2: Call is made directly after variable entry. This step is only _executed if the same variable is not input-ready and could not be filled for I_STEP = 1.
3） I_STEP = 3: In this call, you can check the values of the variables. When an exception (RAISE) is triggered, the variable screen appears again. I_STEP = 2 is then also called again.
4） I_STEP = 0: The enhancement is not called from the variable screen. The call can originate from the authorization check or from the monitor.
I_step = 0 用于权限检查。
I_step = 1 屏幕打开前赋值
I_step = 3 校验