blocks|key|82618|text|而不是foreach循环，您应该这样做|type|unstyled|depth|inlineStyleRanges|entityRanges|data|82619|//+create+comma+separated+list+of+selected+courses
var+courses+=+string.Join(",",+lstCourse.Items
++++++++++++++++++++++++++++++++++++++++.Where(item=>item.Selected)
++++++++++++++++++++++++++++++++++++++++.Select(s=>s.Text)
++++++++++++++++++++++++++++++++++++++++.ToList());+
//+add+courses+as+parameter
com.Parameters.Add("@courses",+SqlDbType.NVarChar).Value+=+courses;|code-block|syntax|javascript|82620|在阅读了您在下面分享了过程代码的注释之后，更新。|offset|length|style|BOLD|82621|update+Student+
set+studentNum=@studentNum,studentName=@studentName,courses=@courses+
where+studentId=@studentId`|82622|您似乎没有将@studentId作为参数传递。这可能是出现错误消息的原因|CODE|82623|82624|过程或函数需要参数，但未提供该参数。|blockquote|82625|82626|82627|因此您应该将此参数添加到sql命令中|82628|com.Parameters.Add("@studentId",+SqlDbType.Int).Value+=+studentId;+--+update+the+dbtype+and+variable+as+per+your+system.|82629|entityMap^0|0|0|L|2|0|0|6|A|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|15|8|@$I|16|J|17|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|18|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|19|8|@$I|1A|J|1B|K|Q]]|9|@]|A|$]]|$1|R|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|S|3|T|5|U|7|1D|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]|$1|X|3|Y|5|6|7|1G|8|@]|9|@]|A|$]]|$1|Z|3|10|5|D|7|1H|8|@]|9|@]|A|$E|F]]|$1|11|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]]|12|$]]

Instead of foreach loop, you should do

<pre><code>// create comma separated list of selected courses
var courses = string.Join(",", lstCourse.Items
 .Where(item=&gt;item.Selected)
 .Select(s=&gt;s.Text)
 .ToList()); 
// add courses as parameter
com.Parameters.Add("@courses", SqlDbType.NVarChar).Value = courses;
</code></pre>

UPDATE
After reading through your one of the comments where you have shared the procedure code below.

<pre><code>update Student 
set studentNum=@studentNum,studentName=@studentName,courses=@courses 
where studentId=@studentId`
</code></pre>

it seems you are not passing the <code>@studentId</code> as parameter. that might be the reason for error message 

<blockquote>
 Procedure or function expects parameter, which was not supplied.
</blockquote>

So you should add this parameter to sql command 

<pre><code>com.Parameters.Add("@studentId", SqlDbType.Int).Value = studentId; -- update the dbtype and variable as per your system.
</code></pre>

blocks|key|2812225|text|错误是正常的|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2812226|对于存储过程的调用，不能多次发送具有相同名称的参数。|2812227|如果需要将课程列表保存到学生实体，则必须更改数据库的结构，并使用带有指向学生表的外键的新表。|2812228|请查看此文档Foreing+Key、Store+Procedure|2812229|entityMap|0|LINK|mutability|MUTABLE|url|https://www.w3schools.com/sql/sql_foreignkey.asp|1|https://www.w3schools.com/sql/sql_stored_procedures.asp^0|0|6|0|0|0|6|B|0|I|F|1|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Y|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|Z|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|10|8|@]|D|@$9|11|A|12|1|13]|$9|14|A|15|1|16]]|E|$]]|$1|L|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]|T|$5|O|P|Q|E|$R|U]]]]

The Error is normal

You can not send more than once a parameter with the same name for the invocation of a stored procedure.

If you need to save a list of courses to the student entity, you must change the structure of the database, and use a new table with a foreign key to the student table.

Check this documentation
<a href="https://www.w3schools.com/sql/sql_foreignkey.asp" rel="nofollow noreferrer">Foreing Key</a> ,
<a href="https://www.w3schools.com/sql/sql_stored_procedures.asp" rel="nofollow noreferrer">Store Procedure</a>

blocks|key|84858|text|我认为@Vinit有正确的答案来做你想做的事情。你想要这个来代替你的foreach+(ListItem+item+in+lstCourse.Items)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|84859|//+create+comma+separated+list+of+selected+courses
var+courses+=+string.Join(",",+lstCourse.Items
++++++++++++++++++++++++++++++++++++.Where(item=>item.Selected)
++++++++++++++++++++++++++++++++++++.Select(s=>s.Text)
++++++++++++++++++++++++++++++++++++.ToList());+
//+add+courses+as+parameter
com.Parameters.Add("@courses",+SqlDbType.NVarChar).Value+=+courses;|code-block|syntax|javascript|84860|它构建逗号分隔的课程名称列表，然后将其作为一个参数@courses放入命令中。|84861|然而！！在这样做了大约20年之后，我可以告诉你，你不会真的喜欢这样做的。您将希望学生选择的课程位于不同的记录中。每次你要处理这些课程时，你都要处理这些课程名称的集合。在这种情况下，我所做的是创建一个单独的表，将学生加入到“多对多”关系中的课程。顺便说一句，我在你的代码中看不到你告诉命令执行哪个SP的地方。|84862|麦克|84863|entityMap^0|Y|16|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|X|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|Y|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|R|$]]

I think @Vinit had the right answer to do what you want to do. In place of your <code>foreach (ListItem item in lstCourse.Items)</code> you want this instead.

<pre><code>// create comma separated list of selected courses
var courses = string.Join(",", lstCourse.Items
 .Where(item=&gt;item.Selected)
 .Select(s=&gt;s.Text)
 .ToList()); 
// add courses as parameter
com.Parameters.Add("@courses", SqlDbType.NVarChar).Value = courses;
</code></pre>

It builds the list of comma separated course names and then puts that into the command as one argument @courses.

However!! After having done this for around 20 years I can tell you you're not really going to like it this way. You're going to want the courses that the student selected to be in separate records. Each time you have to deal with these courses you're going to deal with this collection of course names.
What I have done in this case is create a separate table to join Student to Course in a "Many to Many" relationship.
BTW - I don't see the place in your code where you tell the command what SP to execute.

Mike

I'm trying to update a database table with values from listbox as well as textbox values however and exception was thrown 
Exception.

<blockquote>
 Procedure or function expects parameter, which was not supplied.
</blockquote>

thrown even after supplying the parameter. I wanted the courses selected to be shown in the same column of database table separated by comma.
This is what I have so far.

<pre><code> using (SqlCommand com = new SqlCommand("updateStudent", connection))
 {
 com.CommandType = CommandType.StoredProcedure;

 com.Parameters.AddWithValue("@studentNum", studentNum.Text);

 com.Parameters.Add("@studentName", SqlDbType.NVarChar).Value = studentName.Text;

 foreach (ListItem item in lstCourse.Items)
 {
 if (item.Selected)
 {
 com.Parameters.Add("@courses", SqlDbType.NVarChar).Value = " " + item.Text + " ";
 }
 }
 com.ExecuteNonQuery();
 com.Parameters.Clear();
 }
 }
</code></pre>

how to update database table with listbox values using c#

数据库

我试图用列表框和文本框中的值来更新数据库表，但是异常被抛出了异常。过程或函数需要参数，但未提供该参数。即使在提供参数之后也会抛出。我希望选定的课程显示在数据库表的同一列中，用逗号分隔。这就是我到目前为止所拥有的。 using (SqlCommand com = new SqlCommand("updateStudent...

问如何使用c#使用列表框更新数据库表
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