Datagrid Checkbox Filter Shows Only First Selected Row

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C#

SQL

checkbox

Hi. I have a table in which I had to add the 'checkbox column'. I have a button which needs to filter only SELECTED ROWS. I did my research on the internet and found some different way (creating a new datatable, new columns and storing the data into them) but It is not how I should do it. I want the SQL querry to filter my datagridview so I came up with this code:

private void button2_Click(object sender, EventArgs e)
        {
            
            for ( int i = 0; i < grupeDataGridView.Rows.Count; i++)
            {
                DataGridViewRow row = new DataGridViewRow();
                row = grupeDataGridView.Rows[i];
                
                if (Convert.ToBoolean(row.Cells[0].Value) == true)
                {
                    label1.Text = row.Cells[2].Value.ToString();

                    listBox1.Items.Add(label1.Text);

                    try
                    {
                        this.grupeTableAdapter.FillBy12(this.dbDiplomskiDataSet.grupe, label1.Text);
                    }

                    catch (SystemException ex)
                    {
                       System.Windows.Forms.MessageBox.Show(ex.Message);
                    }
                }
            }
        }

THE PROBLEM: Application filters only ONE ROW and the odd thing is that it shows FIRST SELECTED ROW. I thought if something is wrong and the code shows me only ONE ROW it should be LAST ? Anyway here's the example:

IF I HAVE 10 ROWS, AND I SELECT 2ND, 4TH AND 6TH ROW I WANT THE PROGRAM TO SHOW ME ROWS 2,4,6, AND THIS CODE THAT I'VE WRITTEN SHOWS ME ONLY ROW - 2 ....

Can someone help me how to get rest of the selected rows. Thank you