Example

//connecting to database and copying record to DataAdapter
string strConnection = "Server=abc\\SQLEXPRESs;Database=Employee;Trusted_Connection=True";
            SqlConnection con = new SqlConnection(strConnection);
            con.Open();
            SqlDataAdapter da = new SqlDataAdapter("select * from employee", con);
            DataSet ds = new DataSet();
            da.Fill(ds, "Employee");
            DataTable dt = ds.Tables["Employee"];
            DataRow row;
 
//populating combobox.
 
            for (int i = 0; i < dt.Rows.Count; i++)
            { 
//this will run for all rows present in table.                              
                row = dt.Rows[i];
 
//adding items to combobox one by one.
                cbID.Items.Add(row[0].ToString());
            }