使用SQL Server 2008的Winforms C＃

Question

private void fillcode()
{
    try
    {
        SqlConnection con = new SqlConnection("Data Source=ANISH;Initial Catalog=HM;Integrated Security=True");
        con.Open();
        string s = "select max(CustomerId) as Id from CustomerDetails";
        SqlCommand cmd = new SqlCommand(s, con);
        SqlDataReader dr = cmd.ExecuteReader();
        dr.Read();
        int i = Convert.ToInt16(dr["Id"].ToString());
        sid.Text = (i + 1).ToString();
        con.Close();
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

我正在使用此代码，但是如果我的表中没有数据，将无法接受，这是一个问题。 所以我想使用如果没有数据，则应将CustomerId设置为1

Answer 1

没有行将为NULL ，因此您可以：

"select isnull(max(CustomerId), 1) as Id from CustomerDetails"

您还应该查看为实现单一结果而设计的ExecuteScalar 。

Answer 2

这样尝试

private void fillcode()
{
    try
    {
        SqlConnection con = new SqlConnection("Data Source=ANISH;Initial Catalog=HM;Integrated Security=True");
        con.Open();
        string s = "select max(CustomerId) as Id from CustomerDetails";
        SqlCommand cmd = new SqlCommand(s, con);
        SqlDataReader dr = cmd.ExecuteReader();
        if(dr.Read())
        {
            int i = Convert.ToInt16(dr["Id"].ToString());
            sid.Text = (i + 1).ToString();
        }
        else
        {
            sid.Text = "1"
        } 
        con.Close();
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}