SQL 数据库 If-Else 语句

Question

private void btnChange_Click(object sender, EventArgs e)
{
    con.Open();

    SqlCommand cmd = con.CreateCommand();
    cmd.CommandType = CommandType.Text;
    cmd.CommandText = "update Customer set MembershipPoint='" + textMembershipPoint.Text + "' where NameCustomer='" + textNameCustomer.Text + "'";

    cmd.ExecuteNonQuery();

    if (cmd.ExecuteScalar() != null)
    {
        textMembershipPoint.Text = Convert.ToString(cmd.ExecuteScalar());
    }
    else if (cmd.ExecuteScalar() != )
    {
        MessageBox.Show("Invalid Name of Customer.");
    }
    else if (cmd.ExecuteScalar() != )
    {
        MessageBox.Show("Invalid Membership Point. Only Number Allowed.");
    }
    else
    {
        MessageBox.Show("Membership Point is changed.");
    }

    con.Close();

    display_data();
}

我有一个名为Customer的数据库表， NameCustomer包含ID_Customer 、 NameCustomer和MembershipPoint列。

当客户输入不在Customer表中的名称时，输出将显示“Invalid Name of Customer.”。

如果客户输入无效的 MembershipPoint，输出将显示“Invalid Membership Point. Only Number Allowed.”。

如果一切正常，则输出将显示“Membership Point is changed.”。

谁能告诉我我需要为 if else 语句做些什么才能实现这一目标？

Answer 1

首先，您必须学习使用参数化查询以避免#1 漏洞——SQL 注入！ 这样做 -总是- 没有例外。

其次 - 现在，您正在多次执行UPDATE语句，这非常糟糕......只需执行一次，记录结果，然后仅根据结果进行推理 - 不要多次执行 SQL 命令。

所以尝试这样的事情：

private void btnChange_Click(object sender, EventArgs e)
{
    // check if the membership points text is a valid INT or not
    int membershipPoints = 0;
    
    if (!int.TryParse(textMembershipPoint.Text, out membershipPoints))
    {
        MessageBox.Show("Invalid Membership Point. Only Number Allowed.");
        return;
    }


    // use a properly parametrized query
    string updateQuery = "UPDATE dbo.Customer SET MembershipPoint = @Points WHERE NameCustomer = @CustomerName;";
    
    // put your SqlCommand into a proper "using" block
    using (SqlCommand cmd = new SqlCommand (updateQuery, con))
    {
        // define the parameters and set their values
        cmd.Parameters.Add("@Points", SqlDbType.Int).Value = membershipPoints;
        cmd.Parameters.Add("@CustomerName", SqlDbType.VarChar, 100).Value = textNameCustomer.Text;
        
        // open connection, execute UPDATE, record number of rows updated, close connection
        con.Open();
        int rowsUpdated = cmd.ExecuteNonQuery();
        con.Close();
        
        // now reason just on the result
        if (rowsUpdated > 0)
        {
            // some rows were updated --> success
            MessageBox.Show("Success - rows updated");
        }
        else
        {
            // no rows were updated --> 
            MessageBox.Show("No rows updated - most likely invalid customer name");
        }
    }
    
    
    display_data();
}