Save data from datagrid to SQL all at once

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C#

SQL

Hi I have a winform app in c# witch permits edditing of tables from my sql database. I managed to get the tables opened and edit them but when i save the data all lines get replicated. Is there a way to do this but only edit the required fields or insert if a new one is added? I tried the update command but it wont work. the code i use is:

What I have tried:

using (SqlConnection con = new SqlConnection(cs))
 {
     con.Open();
     foreach (DataGridViewRow row in dataGridView1.Rows)
     {

         if (!row.IsNewRow)
         {
             using (SqlCommand cmd = new SqlCommand("INSERT INTO temp (data1, data2, data3, data4) VALUES(@c1,@c2,@c3,@c4)", con))
             {

                 cmd.Parameters.AddWithValue("@C1", row.Cells[0].Value);
                 cmd.Parameters.AddWithValue("@C2", row.Cells[1].Value);
                 cmd.Parameters.AddWithValue("@C3", row.Cells[2].Value);
                 cmd.Parameters.AddWithValue("@C4", row.Cells[3].Value);

                 cmd.ExecuteNonQuery();

             }
         }
     }
 }