什么是从数据表的列中找到最小的代码。我已经为此编写代码但是我得到错误代码如下所示 [英] What Is The Code For Finding Smallest No From The Column Of Datatable .I Have Write The Code For This But I Got Error That Code Is Shown Below

问题描述

con = new SqlConnection(cs);
             con.Open();
             cmd = con.CreateCommand();
             cmd = new SqlCommand("select distinct RTRIM(FundLeft) from Invoice ", con);
             rdr = cmd.ExecuteReader();
             while (rdr.Read())
             {
                 DataRow[] dr = dt.Select("FundLeft = MIN(FundLeft)");
                 txtfundleft.Text = dr[0][1].ToString();
             }
             con.Close();

推荐答案

嗯......有很多东西这里错了。

首先，在你的SQL中使用RTRIM意味着FundLeft存储为VARCHAR或NVARCHAR值 - 这很容易做到，但如果你试图将它用作数值，就像你在这里一样。根据需要将其作为数值存储在INT或FLOAT中。它可能看起来更复杂，但从长远来看它会容易得多。



其次，你根本没有使用你从数据库中读取的数据：你设置一个阅读器，然后忽略它的价值，支持看起来像DataTable的东西。



我觉得你刚才在这里猜到了，而你真的没有坐下来想想你需要做什么。这种方法不起作用：你真的，真的需要停下来，坐下来找出你想要做的事情以及你真正需要做的事情。

我不能建议任何具体的改进来摆脱错误，因为据我所知，没有任何东西可以实际做任何你的任务！



以后：如果你收到错误 - 告诉我们这条消息是什么，以及它出现在哪一行？

Um...There are quite a lot of things wrong here.
Firstly, the use of RTRIM in your SQL implies that FundLeft is stored as a VARCHAR or NVARCHAR value - which is simple to do, but causes massive problems if you try to use it as a numeric value, as you are here. Store it as a numeric value in an INT or FLOAT as appropriate. It may seem more complex, but it's a lot easier in the long run.

Secondly, You aren't using the data you read from the DB at all: you set up a reader, and then ignore it's value in favour of what appears to be a DataTable.

I get the feeling that you have just guessed here, and that you really haven't sat down and thought about what you need to do. That approach won't work: you really, really need to stop, sit back and work out what you are trying to do and how you actually need to do it.
I can't suggest any specific improvements to get rid of the error, because as far as I can see, there is nothing there that will actually do whatever your task is!

And in future: if you get an error - tell us what the message is, and exactly which line it appears on?

而不是你的选择不同的查询只需使用

Rather than your "select distinct" query just use

select min(FundLeft) as FundLeft from Invoice

然后使用 cmd.ExecuteScalar [ ^ ]读取结果。

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