我有以下代码：
dbConnection cn = new dbConnection();
SqlCommand cmd = new SqlCommand();
protected void dropdown_student_SelectedIndexChanged(object sender, EventArgs e)
{
string StudentGUID = dropdown_student.SelectedValue;
cn.con.Open();
cn.cmd.Connection = cn.con;
cn.cmd.CommandText = "select SUM(Marks) AS 'Total' from Marksheet where StudentGUID = " + StudentGUID + " ";
dr = cn.cmd.ExecuteReader();
if (dr.HasRows)
{
while (dr.Read())
{
textbox_total.Text = dr["Total"].ToString();
}
cn.con.Close();
}
}
我想在文本框中显示总分数值，但它不起作用。谁能指出我正确的方向？
尝试这样的事情：
// define your query upfront - using a PARAMETER!
string query = "SELECT SUM(Marks) FROM dbo.Marksheet WHERE StudentGUID = @StudentID;";
// put the SqlConnection and SqlCommand into using blocks
using (dbConnection cn = new dbConnection())
using (SqlCommand cmd = new SqlCommand(query, cn))
{
// define the parameter value
cmd.Parameters.Add("@StudentID", SqlDbType.UniqueIdentifier).Value = dropdown_student.SelectedValue;
cn.Open();
// use ExecuteScalar if you fetch one row, one column exactly
object result = cmd.ExecuteScalar();
cn.Close();
if(result != null)
{
int value = (int)result;
textbox_total.Text = value.ToString();
}
}
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