How To Check If Data Already Exists In Database?

I was able to get this code to work but now I get a SQL error if you try to submit the same information twice. 
How can I add a message saying that the "email" already exists in database without the SQL error?
 

    protected void Button1_Click1(object sender, EventArgs e)
    {
        SqlConnection conn =
            new SqlConnection("Data Source=TECATE;Initial Catalog=subscribe_mainSQL; User Id=maindb Password=123456; Integrated Security=SSPI");
        SqlCommand cmd = new SqlCommand("INSERT INTO [main] (, [userid], [fname], [lname], [degree]) VALUES (@email, @userid, @fname, @lname, @degree)", conn);
       
            conn.Open();
            cmd.Parameters.AddWithValue("@email", email.Text);
            cmd.Parameters.AddWithValue("@userid", uscid.Text);
            cmd.Parameters.AddWithValue("@fname", fname.Text);
            cmd.Parameters.AddWithValue("@lname", lname.Text);
            cmd.Parameters.AddWithValue("@degree", degree.SelectedItem.Value);

            int i = cmd.ExecuteNonQuery();

            conn.Dispose();
        }
   

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Hi,

I'm wondering is there a command that I can use to check if a certain value exists in the database? Something that returns true or false perhaps?

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hi,

 

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For any Database like (MS Access, Oracle, MS SQL-Server,MySQL)..

 

Please help me.....

 

thank's in advance.......

Paresh Patel.

Paresh.onmail@hotmail.com

 

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