SELECT 
  PI.product_id, 
  F1.id AS file_id, 
  F1.path AS file, 
  (
    SELECT 
      PI1.alt 
    FROM 
      `cscart_products__images` PI1 
    WHERE 
      PI1.original_file_id = F1.id
  ) AS file_alt, 
  F2.id AS big_file_id, 
  F2.path AS big_file, 
  (
    SELECT 
      PI2.alt 
    FROM 
      `cscart_products__images` PI2 
    WHERE 
      PI2.watermark_big_file_id = F2.id
  ) AS big_file_alt, 
  F3.id AS small_file_id, 
  F3.path AS small_file, 
  (
    SELECT 
      PI3.alt 
    FROM 
      `cscart_products__images` PI3 
    WHERE 
      PI3.watermark_small_file_id = F3.id
  ) AS small_file_alt 
FROM 
  `cscart_products__images` AS `PI` 
  LEFT JOIN `files` AS `F1` ON `F1`.`id` = `PI`.`original_file_id` 
  LEFT JOIN `files` AS `F2` ON `F2`.`id` = `PI`.`watermark_big_file_id` 
  LEFT JOIN `files` AS `F3` ON `F3`.`id` = `PI`.`watermark_small_file_id` 
WHERE 
  `PI`.`product_id` = 32402

Query time 0.00153

Result

product_id file_id file file_alt big_file_id big_file big_file_alt small_file_id small_file small_file_alt
32402 403402 https://s3.timeweb.cloud/482029f9-prod/products__images/32402_3c576b0e79a3_32431_83519cbecaf1_%25D0%25A1%25D0%25BC%25D0%25BE%25D1%2582%25D1%2580%25D0%25B5%25D1%2582%25D1%258C%2520%25D0%25BD%25D0%25B5%25D0%25B4%25D0%25B0%25D0%25B2%25D0%25BD%25D0%25B8%25D0%25B5%2520%25D1%2584%25D0%25BE%25D1%2582%25D0%25BE%25281%2529.jpeg 403403 https://s3.timeweb.cloud/482029f9-prod/products__images/32402_eb5a918fd5bf_32431_83519cbecaf1_%25D0%25A1%25D0%25BC%25D0%25BE%25D1%2582%25D1%2580%25D0%25B5%25D1%2582%25D1%258C%2520%25D0%25BD%25D0%25B5%25D0%25B4%25D0%25B0%25D0%25B2%25D0%25BD%25D0%25B8%25D0%25B5%2520%25D1%2584%25D0%25BE%25D1%2582%25D0%25BE%25281%2529.webp 403404 https://s3.timeweb.cloud/482029f9-prod/products__images/32402_90a220766ce8_32431_83519cbecaf1_%25D0%25A1%25D0%25BC%25D0%25BE%25D1%2582%25D1%2580%25D0%25B5%25D1%2582%25D1%258C%2520%25D0%25BD%25D0%25B5%25D0%25B4%25D0%25B0%25D0%25B2%25D0%25BD%25D0%25B8%25D0%25B5%2520%25D1%2584%25D0%25BE%25D1%2582%25D0%25BE%25281%2529.webp