SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    20813, 20814, 20815, 20816, 20817, 20818, 
    20819, 20820, 20821, 20822, 20823, 
    20824, 20825, 20826, 20827, 20828
  )

Query time 0.00036

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_products",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (20813,20814,20815,20816,20817,20818,20819,20820,20821,20822,20823,20824,20825,20826,20827,20828)"
    }
  }
}