Сравнение дат DATEDIFF

            public void SelectDB2DataGridView(DataTable result, DataGridView dataGridView1, string sql_query)
            {
                string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + ExePath + "\\res\\Lamps.mdb;Jet OLEDB:Engine Type=5;Jet OLEDB:Database Password=Пароль";
                OleDbConnection connection = new OleDbConnection(connectionString);
                connection.Open();
                OleDbCommand OleDbComm = new OleDbCommand(sql_query, connection);
                OleDbDataAdapter adapter = new OleDbDataAdapter(OleDbComm);
                adapter.Fill(result);
                dataGridView1.DataSource = result;
                OleDbComm.ExecuteNonQuery();                
                connection.Close();
            }

DB DB3 = new DB();
            DataTable result_lock = new DataTable();
            string DateNow_lock = DateTime.Now.ToShortDateString();
 
            string sql_lock = "SELECT issue_date, material, destination FROM materials WHERE DATEDIFF(mm, issue_date, '" + DateNow_lock + "') <= 3 ORDER BY number";
 
            DB3.SelectDB2DataGridView(result_lock, dataGridView3, sql_lock);
            dataGridView3.Columns[0].HeaderText = "Материал";
            dataGridView3.Columns[1].HeaderText = "Назначение";
            //Итого 157                
            dataGridView3.Columns[0].Width = 78; //Материал 
            dataGridView3.Columns[1].Width = 80; //Назначение

adapter.Fill(result)

string sql_lock = "SELECT material, destination FROM materials WHERE (YEAR(DATE()) - YEAR(issue_date) <= 1) and " +
"(MONTH(DATE()) - MONTH(issue_date) <=3 or MONTH(DATE()) - MONTH(issue_date) >=10) ORDER BY number";