SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    12656, 12655, 12646, 12631, 12998, 12997, 
    12996, 12995, 10826, 10825, 10824, 
    10823, 10822, 10821, 10820, 10819, 
    10818, 10817, 10816, 10815
  )

Query time 0.00093

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": 20,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (12656,12655,12646,12631,12998,12997,12996,12995,10826,10825,10824,10823,10822,10821,10820,10819,10818,10817,10816,10815)"
    }
  }
}