SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    9839, 12702, 9841, 9848, 9840, 9844, 
    9843, 9846, 9845, 9860, 9859, 9857, 
    9852, 9861, 9862, 9847, 9863, 9856, 
    9855, 9838
  )

Query time 0.00092

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 (9839,12702,9841,9848,9840,9844,9843,9846,9845,9860,9859,9857,9852,9861,9862,9847,9863,9856,9855,9838)"
    }
  }
}