SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    3993, 4002, 3991, 3992, 3996, 3998, 3986, 
    3994, 4003, 3997, 3990
  )

Query time 0.00026

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": 11,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (3993,4002,3991,3992,3996,3998,3986,3994,4003,3997,3990)"
    }
  }
}