SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    3900, 3901, 3913, 116, 3909, 3910, 3911, 
    120, 118, 3914, 3912, 3897, 53, 5881, 
    3898, 3899
  )

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 (3900,3901,3913,116,3909,3910,3911,120,118,3914,3912,3897,53,5881,3898,3899)"
    }
  }
}