SELECT 
  product_id, 
  amount 
FROM 
  cscart_warehouses_sum_products_amount 
WHERE 
  1 
  AND product_id IN (104, 29, 101, 103, 102)

Query time 0.00034

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "5.76"
    },
    "table": {
      "table_name": "cscart_warehouses_sum_products_amount",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 10,
      "rows_produced_per_join": 10,
      "filtered": "100.00",
      "index_condition": "(`test_uchur_k`.`cscart_warehouses_sum_products_amount`.`product_id` in (104,29,101,103,102))",
      "cost_info": {
        "read_cost": "4.76",
        "eval_cost": "1.00",
        "prefix_cost": "5.76",
        "data_read_per_join": "160"
      },
      "used_columns": [
        "product_id",
        "amount"
      ]
    }
  }
}