How to read and compare data from an SQL Server Express database

Question

I am trying to create a select statement in C# to check if the value inserted into a textbox (userName) is in an existing SQL database. I have a database called Employee containing a table called EVUSERS and it has a column called UName.

In my code I have a method which takes the value from a textbox called UserBox. I would like to know if there is a temporary table where the select is stored which I can compare the textbox value to.

Here is the code:

private void CheckLoginExist()
{
            String userName = UserBox.Text;

            string connectionString = @"Data Source=.\SQLEXPRESS;Database=Employee;Integrated Security=true";
            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                using (SqlCommand command = connection.CreateCommand())
                {

                    command.CommandText = "SELECT UName FROM EVUSERS WHERE UName = @UName";
                    command.Parameters.AddWithValue("@UName", userName);
                    connection.Open();
                    command.ExecuteNonQuery();
                    connection.Close();
                }
            }
}

I currently have a select but I am not sure how to display it and I am able to connect to the DB.

Your returning a single value (or null) so use `ExecuteScalar` as `ExecuteNonQuery` is for non-queries (which includes `select`) — Alex K., Jan 23 '14 at 15:21
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Marko Juvančič · Accepted Answer · 2014-01-24T15:48:53.963

1

You need ExecuteScalar, not ExecuteNonQuery

...
connection.Open();
var name = command.ExecuteScaclar().ToString();
connection.Close();

if (name != null) {
  MessageBox.Show("This name already exists");
  return;
}

edited Jan 24 '14 at 15:48

answered Jan 23 '14 at 15:22

Marko Juvančič

5,792
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score 0 · Answer 2 · answered Jan 23 '14 at 15:21

0

private void CheckLoginExist()
{
    DataTable dt = new DataTable();
    String userName = UserBox.Text;

   string connectionString = @"Data Source=.\SQLEXPRESS;Database=Employee;Integrated Security=true";
   using (SqlConnection connection = new SqlConnection(connectionString))
   {
         SqlDataAdapter da = new SqlDataAdapter("SELECT UName FROM EVUSERS WHERE UName = '" + userName  + "'", _conn);                 
         da.Fill(dt); 
   }
}

Now you can do whatever you want to do with this DataTable.

answered Jan 23 '14 at 15:21

Abdur Rahim

3,975
14
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83

Thanks. How would I perhaps, display in an if statement displaying a messagebox if it returns true? What would be the argument that I would use? if(userName == this.userName) { MessageBox.Show("Match"); } thanks – Jan 23 '14 at 15:42
How can I test this, to see if I have an existing username in the database. If I enter a value into the textbox which exists in the database, What can parameter I use that will check it. If I want a messagebox to pop up saying that username exists? Thank you again – Jan 23 '14 at 15:47

How to read and compare data from an SQL Server Express database

2 Answers2