Using condition inside a while loop in C#

Question

I have a problem with my C# code.

I need validating the user name, I used an if-condition inside the while loop but the thing is that even when the username and password are incorrect, it not executes any statement.

I have tested the query of authentication in database and the output is correct.

I've tried using these three different solutions without success.

Here is my code :

Solution #1

using (OdbcDataReader reader = command.ExecuteReader())
{
    while (reader.Read())
    {
        int count = reader.GetInt32(0);

        if (count > 0)
        {
            Response.Write("Welcome!");
        }
        else
        {
            Page.ClientScript.RegisterStartupScript(this.GetType(), "Alert", "alert('no data.');", true);
        }
    }
}

Solution #2

using (OdbcDataReader reader = command.ExecuteReader())
{
    while (reader.Read())
    {
        if (reader.HasRows)
        {
            Response.Write("Welcome!");
        }
        else
        {
            Page.ClientScript.RegisterStartupScript(this.GetType(), "Alert", "alert('no data.');", true);
        }
    }
}

Solution #3

using (OdbcDataReader reader = command.ExecuteReader())
{
    while (reader.Read())
    {
        if (!String.IsNullOrEmpty(reader[0].ToString()))
        {
            Response.Write("Welcome!");
        }
        else
        {
            Page.ClientScript.RegisterStartupScript(this.GetType(), "Alert", "alert('no data.');", true);
        }
    }
}

Answer 1

None of your solutions are valid. You seem to think that your while loop is always executed, however this is not the case. When your sql query returns 0 rows you never enter the while(reader.Read()) loop.

A simple approach, based on your second solution, could be something like the following:

using (OdbcDataReader reader = command.ExecuteReader())
{

    if (reader.HasRows)
    {
        Response.Write("Welcome!");
    }
    else
    {
        Page.ClientScript.RegisterStartupScript(this.GetType(), "Alert", "alert('no data.');", true);
    }
}

Note how there is no while loop involved.