如何从字符串中删除字符的最后一个实例

I am building a string with StringBuilder.

我正在使用StringBuilder构建一个字符串。

StringBuilder Q = new StringBuilder();
Q.Append("INSERT INTO ");
Q.Append(_lstview_item);
Q.Append(" VALUES");
Q.Append("("); 
for (i = 0; i < col_no; i++)
{
    Q.Append("'");
    Q.Append(col_value[i]);
    Q.Append("'");
    Q.Append(",");
} 
Q.Append(")");
string query = Q.ToString();

However, I am getting a "," at the end of my string. I tried using

但是,我的字符串末尾有一个“,”。我试过用

string query = ext.Substring(0, ext.LastIndexOf(",") + 1);

to remove the surplus ",", but this also removes the ")".

删除剩余的“,”,但这也删除了“)”。

How can I remove the last comma only?

如何仅删除最后一个逗号?

actual outcome : INSERT INTO .... VALUES('1','2','3',)

实际结果:INSERT INTO .... VALUES('1','2','3',)

desired outcome : INSERT INTO .... VALUES('1','2','3')

期望的结果:INSERT INTO .... VALUES('1','2','3')

6 个解决方案

#1

This:

Q.Append(")");

replace with

if (col_no > 0)
{
    Q.Length--;
}

Q.Append(")");

The check if (col_no > 0) is a little overboard, because if there is no column, the query will still fail for other reasons, but if we consider this a template on how to combine strings in a StringBuilder, then the check is the right thing to do.

检查if(col_no> 0)是否有点过分,因为如果没有列,查询仍会因其他原因而失败,但如果我们认为这是一个关于如何在StringBuilder中组合字符串的模板,那么检查就是正确的事情。

Ah... Building a query in that way is the wrong thing to do.

啊......以这种方式构建查询是错误的。

#2

You can use the "Remove" method to remove a specific character at a position:

您可以使用“删除”方法删除某个位置的特定字符:

query = query.Remove(query.LastIndexOf(","), 1);

#3

I would suggest to remove the comma first before you add the last ), so:

我建议在添加最后一个之前先删除逗号,所以:

for (i = 0; i < col_no; i++)
{
    Q.Append("'");
    Q.Append(col_value[i]);
    Q.Append("'");
    Q.Append(",");

} 
if(col_no > 0) Q.Length --; // <-- this removes the last character
Q.Append(")");
string query = Q.ToString();

However, if you really want to create a sql-query i would strongly suggest to use sql-parameters to prevent sql-injection. So don't include the values in your sql-string.

但是,如果你真的想创建一个sql-query,我强烈建议使用sql-parameters来阻止sql-injection。所以不要在sql-string中包含这些值。

#4

the correct way to achieve your goal is to use a parameterized query.

实现目标的正确方法是使用参数化查询。

there is the possibility to delete the last coma before putting the bracket

在放置括号之前,有可能删除最后一个昏迷

the pure answer to your question can be this:

对你的问题的纯粹答案可以是这样的:

string query = ext.Substring(0, ext.LastIndexOf(",")) + ext.Substring(ext.LastIndexOf(",") + 1);

or this:

string query = ext.Remove(ext.LastIndexOf(","), 1);

#5

Try this. simple logic

尝试这个。简单的逻辑

Check the below if condition in befor append comma line

检查以下条件是否为befor append逗号行

                  **if(i!=(col_no-1))
                    {
                    Q.Append(",");
                    }*

With your code .

用你的代码。

                 for (i = 0; i < col_no; i++)
                  {
                    Q.Append("'");
                    Q.Append(col_value[i]);
                    Q.Append("'");
                    **if(i!=(col_no-1))
                    {
                    Q.Append(",");
                    }**

                  }

#6

Replace

            Q.Append(",");

inside the for-loop with

在for循环中用

            if (i != col_no - 1)
            {
                Q.Append(",");
            }

#1