SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    9984, 9985, 9986, 9987, 9988, 9989, 9990, 
    9991, 9992, 9993, 9994, 9995, 9996, 
    9997, 9998, 9999, 12995, 12996, 12997, 
    12998
  )

Query time 0.00044

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 (9984,9985,9986,9987,9988,9989,9990,9991,9992,9993,9994,9995,9996,9997,9998,9999,12995,12996,12997,12998)"
    }
  }
}