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SELECT 
  cscart_multi_decproduct_files.*, 
  cscart_multi_decproduct_file_descriptions.file_name, 
  cscart_multi_decproduct_file_descriptions.license, 
  cscart_multi_decproduct_file_descriptions.readme 
FROM 
  cscart_multi_decproduct_files 
  LEFT JOIN cscart_multi_decproduct_file_descriptions ON cscart_multi_decproduct_file_descriptions.file_id = cscart_multi_decproduct_files.file_id 
  AND cscart_multi_decproduct_file_descriptions.lang_code = 'ru' 
WHERE 
  1 = 1 
  AND cscart_multi_decproduct_files.product_id = 49 
  AND preview_path != '' 
  AND cscart_multi_decproduct_files.status = 'A' 
ORDER BY 
  cscart_multi_decproduct_files.position asc, 
  cscart_multi_decproduct_file_descriptions.file_name asc

Query time 0.00061

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}