SELECT 
  `F`.`path`, 
  `PI`.`product_id`, 
  `PI`.`alt` 
FROM 
  `cscart_products__images` AS `PI` 
  LEFT JOIN `files` AS `F` ON `PI`.`watermark_small_file_id` = `F`.`id` 
WHERE 
  `PI`.`product_id` IN ('32408')

Query time 0.00036

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "4.30"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "PI",
          "access_type": "ref",
          "possible_keys": [
            "product_id"
          ],
          "key": "product_id",
          "used_key_parts": [
            "product_id"
          ],
          "key_length": "3",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 4,
          "rows_produced_per_join": 4,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "1.00",
            "eval_cost": "0.40",
            "prefix_cost": "1.40",
            "data_read_per_join": "128"
          },
          "used_columns": [
            "product_id",
            "watermark_small_file_id",
            "alt"
          ]
        }
      },
      {
        "table": {
          "table_name": "F",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "id"
          ],
          "key_length": "4",
          "ref": [
            "dev2.PI.watermark_small_file_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 4,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "2.50",
            "eval_cost": "0.40",
            "prefix_cost": "4.30",
            "data_read_per_join": "14K"
          },
          "used_columns": [
            "id",
            "path"
          ]
        }
      }
    ]
  }
}

Result

path product_id alt
https://s3.timeweb.cloud/482029f9-prod/products__images/32408_03108c99a0ee_33434_1cb35d9eb1ae_32408_b55d548d34c4_32409_94ee05be99a9_0_0c14a3436e27_7dd960cc-1c87-49f7-ba90-a2a1 32408
https://s3.timeweb.cloud/482029f9-prod/products__images/32408_3c7291e3a820_33434_004f7de78389_32408_37f9bacc81ab_32409_c49bb443419c_0_04eeb904e3a3_78986c11-a865-4049-b3da-bbf2 32408
https://s3.timeweb.cloud/482029f9-prod/products__images/32408_7abe74dc5bba_33434_6fce87d1c7b5_32408_97958c7b7cfd_32409_4a267b2cf9c0_0_20730aeae61d_42a9ad47-ab22-488c-a1d6-8773 32408
https://s3.timeweb.cloud/482029f9-prod/products__images/32408_dd5729dc6098_33434_7ec55de5548e_32408_fc4ab4893769_32409_981d53ddc493_0_8d48ea09e106_eb26f3ab-709e-47cd-97d3-88f0 32408