how to delete all rows from datagridview in c# and SQL code example

Example: how to delete row in datagrid view in c#

private void btnDelete_Click(object sender, EventArgs e)
{
    if (this.dataGridView1.SelectedRows.Count > 0)
    {
        dataGridView1.Rows.RemoveAt(this.dataGridView1.SelectedRows[0].Index);
    }                
}