如何在数据集中获取最小和最大列数？ [英] How to get min and max columns count in dataset?

问题描述

我在datatable中添加了两个新列，并在这两列中打印了datatable列的最大和最小数量。如何做。我将尝试下面的代码。



我尝试了什么：

I had add two new column to datatable and print the maximum and minimum count of datatable column in this two columns how to do.i will try the below code.

What I have tried:

ds.Tables[k].Columns.Add("Column52");
ds.Tables["Source" + c].AcceptChanges();
for (int f = 0; f < ds.Tables[k].Rows.Count; f++)
{
ds.Tables[k].Rows[f]["Column52"] =ds.Tables[k].Compute("MAX(Column52)","");
//double maxval = Convert.ToDouble((ds.Tables[k].Compute("MAX(Column52)", "")));
}

i试图添加新列并获取最大列数但是

对象无法从DBNull转换为其他类型。

发生异常错误。

i have tried to add new column and get maximum column count but
Object cannot be cast from DBNull to other types.
Exception error occur.

推荐答案

这里有两个问题：第一个问题是，正如Karthik Bangalore所说，这将显示新列的所有行中的最大值，您说这是你不想要的。但这就是计算列的作用：在每一行中显示一个值。所以，如果这不是你想要的，那么你需要重新思考你正在做的事情，并且可能完全找到另一种方式 - 这不涉及新专栏！



另一个是Column52的数据是一个NULLable列，并且您正在尝试将NULL值转换为double值，这在DBNull传播数据以产生NULL结果时不起作用。检查您的数据：为什么您想要成为数字的列中有NULL值？

There are two problems here: the first is that as Karthik Bangalore says, that will show the Maximum value in all rows of the new column, which you say you don't want. But that's what a computed column will do: show a value in every row. So if that isn't what you want, then you need to rethink what you are doing and probably find another way altogether - that doesn't involve a new column!

The other is that your data for "Column52" is a NULLable column, and you are trying to convert NULL values to a double value, which won't work as DBNull propagates through data to produce a NULL result. Check your data: why have you got NULL values in a column you want to be numeric?

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