SELECT SQL Statement for a datagridview

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C#

SQL-Server

selection

Hello, I am inserting Records in a Database. I need my records to be shown in a Datagridview, when a button is pressed. Datagridview should show records only with SensorValue is < 20.
I know, that SELECT, from where statement will be used but dont know , how should i use it here.
Thank you

try
{

  SqlConnection sqlconn = new SqlConnection("Data Source=AN-PC;Initial Catalog=Feb12;Integrated Security=True");
 SqlDataAdapter sa = new SqlDataAdapter();

 string query;

 query = "insert into Table_1( SensorID,SensorValue,DateTime) values( @TM, @NT, @MN)";

    sa.InsertCommand = new SqlCommand(query, sqlconn);
    sa.InsertCommand.Parameters.AddWithValue("@TM", y);
    sa.InsertCommand.Parameters.AddWithValue("@NT", x);
    sa.InsertCommand.Parameters.AddWithValue("@MN", DateTime.Now.ToString());    
                                                                       
    sqlconn.Open();
    try
    {
        sa.InsertCommand.ExecuteNonQuery();
    }
    catch (FormatException ex) { MessageBox.Show(ex.Message); }

    feb12DataSet.GetChanges();

    table_1TableAdapter4.Fill(feb12DataSet.Table_1);

    
    sqlconn.Close();
}
catch (SqlException ea) { MessageBox.Show(ea.Message); }