using System.Data.SqlClient;

SqlConnection Baglanti =new SqlConnection();

Baglanti.ConnectionString
Baglanti.Open();

SqlCommand vericek = new SqlCommand();
vericek.Connection = baglanti;
vericek.CommandText = "select * from OnlineHile";
vericek.CommandType = CommandType.Text;

vericek.ExecuteScalar();

DataTable dtProd = new DataTable();
SqlDataAdapter sqDa = new SqlDataAdapter();

sqDa.Fill(dtProd);

dataGridView1.DataSource = dtProd;

sqlConn.ConnectionString = "server=localhost;user=sa;pwd=a;database=Onlinehile;";