C＃中出现错误

问题描述

我试图总结一些项目的数量，所以我写了一个for循环。

因为我在sql quey和executioncalar（）的帮助下获取了itemid和item的最大值这两个值存储在numlow和numhigh变量中。

我在I中存储了numlow值，而我在for循环中使用了i。
当我运行时
代码一切正常如下

< pre> for（int i = lownum; i< = highnum; ++ i）
 {
 con.Close（）; 
 con.Open（）; 

 SqlCommand qty = new SqlCommand（从invDB中选择itmqty，其中itemid ='+ i + ''，con）; 
 double quant = Convert.ToDouble（qty.ExecuteScalar（））; 

当我将sum（）添加到itmqty时总和（itmqty）它显示错误

。其中数量也为零。

错误是

对象无法从DBNull转换为其他类型

我尝试过：



我用google搜索但没有合适的结果。

解决方案

I am trying to sum the quantity of some items so I wrote one for loop.
for that I took max of itemid and min of itemid with the help of sql quey and executescalar() and that two values stored in numlow and numhigh variables.
I stored numlow value in "I" and that "i" i am using in for loop.
when I am running the code everything is ok like below

<pre> for (int i = lownum; i<= highnum; ++i)
            {
                con.Close();
con.Open();

SqlCommand qty = new SqlCommand("select itmqty from invDB where itemid='"+i+"'", con);
                double quant = Convert.ToDouble(qty.ExecuteScalar());

when I added sum() to that itmqty like sum(itmqty) it is showing error

.Some where quantity is zero also.
Error is "

Object cannot be cast from DBNull to other types"

What I have tried:

I googled but came with no suitable results.

解决方案

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