如何使用更新ADO网 [英] How to use UPDATE in ado net
问题描述
我需要执行一个表(作业)的更新。但它不只是更换用新的一个旧值;在列中已经存在的价值我要补充(SUM)的新值(列的类型为int)。 这是我做的这么远,但我坚持:
I need to perform an update in a table(Homework). But it is not just replacing an old value with a new one; to the already existing value in the column i have to add(SUM) the new value(the column is of type int). This is what i did so far but i am stuck:
protected void subscribeButton_Click(object sender, EventArgs e)
{
string txtStudent = (selectedStudentLabel.Text.Split(' '))[0];
int studentIndex = 0;
studentIndex = Convert.ToInt32(txtStudent.Trim());
SqlConnection conn = new SqlConnection("Server=.\\SQLEXPRESS;AttachDbFilename=|DataDirectory|\\Database.mdf;Trusted_Connection=True;User Instance=yes");
conn.Open();
string sql2 = "UPDATE student SET moneyspent = " + ?????? + " WHERE id=" + studentIndex + ";";
SqlCommand myCommand2 = new SqlCommand(sql2, conn);
try
{
conn.Open();
myCommand2.ExecuteNonQuery();
}
catch (Exception ex)
{
Console.WriteLine("Error: " + ex);
}
finally
{
conn.Close();
}
}
我应该怎么增加这一翻译的 ??? 实现我的目标是什么?
What should i add intead of ??? to achieve my goal?
是否有可能做这种方式?我想避免使用许多查询。
Is it possible to do it this way? I want to avoid using to many queries.
推荐答案
如果我理解正确的话(我不知道我这样做),你希望是这样的:
If i understand you correctly (i'm not sure i do) you want something like this:
string sql2 = "UPDATE student SET moneyspent = moneyspent + @spent WHERE id=@id";
SqlCommand myCommand2 = new SqlCommand(sql2, conn);
myCommand2.Parameters.AddWithValue("@spent", 50 )
myCommand2.Parameters.AddWithValue("@id", 1 )
请注意我用的参数,而不是字符串连接,非常重要!
Notice how i've used parameters and not string concatenation, very important!!
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