SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    323, 324, 328, 329, 330, 535, 333, 390, 
    280, 689, 281, 283, 641, 309, 691, 693
  )

Query time 0.00039

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 (323,324,328,329,330,535,333,390,280,689,281,283,641,309,691,693)"
    }
  }
}