SELECT 
  count(*) 
FROM 
  cscart_ec_table_booking_system 
WHERE 
  booking_type != 'N' 
  AND product_id = 389643

Query time 0.00071

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "Impossible WHERE noticed after reading const tables"
  }
}