How to update data from datagridview with one column to database with two columns? error - cannot insert value null

See more:

C#

SQL

DataGridView

I'm trying to update data from DataGridView to my database. While I was looking for the solution of this problem on google, I noticed that all of the solutions are managed by using class variables (for DataTable,SqlDataAdapter,...). I'm trying to do this just by using function variables.

This is how I loaded data to `DataGridView`:

private void LoadDataGridView(int ID)
    {
        try
        {
             SqlConnection connection = new SqlConnection(connString);
             SqlCommand cmd = new SqlCommand("SELECT SENTENCE FROM Sentences WHERE CategoryID = '" + ID + "'",connection);

             DataTable dataTable = new DataTable();

             SqlDataAdapter dataAdapter = new SqlDataAdapter(cmd);
             dataAdapter.Fill(dataTable);

             DataGridView.DataSource = dataTable;
        }
        catch (Exception)
        {
             MessageBox.Show("ERROR WHILE CONNECTING TO DATABASE!");
        }
    }

DataGridView is showing just those sentences that match particular ID.

What I have tried:

This is what I have tried so far:

private void RefreshBtn_Click(object sender, EventArgs e)
    {
        try
        {
              SqlConnection connection = new SqlConnection(connString);
              SqlCommand cmd = new SqlCommand("SELECT QUESTION FROM Questions WHERE CategoryID IN('" + CategoryID + "')", connection);

              SqlDataAdapter dataAdapter = new SqlDataAdapter(cmd);
              SqlCommandBuilder cmdBuilder = new SqlCommandBuilder(dataAdapter);
              dataAdapter.Update(dataTable);
        }
        catch (Exception)
        {
              MessageBox.Show("ERROR WHILE CONNECTING WITH DATABASE!");
        }
    }

This is the error that comes up:

Cannot insert value NULL into column CategoryID, table ...;column does not allow nulls.Insert fails. The statement has been terminated.<br />