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SELECT 
  cscart_product_files.*, 
  cscart_product_file_descriptions.file_name, 
  cscart_product_file_descriptions.license, 
  cscart_product_file_descriptions.readme 
FROM 
  cscart_product_files 
  LEFT JOIN cscart_product_file_descriptions ON cscart_product_file_descriptions.file_id = cscart_product_files.file_id 
  AND cscart_product_file_descriptions.lang_code = 'en' 
WHERE 
  1 = 1 
  AND cscart_product_files.product_id = 46579 
  AND preview_path != '' 
  AND cscart_product_files.status = 'A' 
ORDER BY 
  cscart_product_files.position asc, 
  cscart_product_file_descriptions.file_name asc

Query time 0.00060

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	cscart_product_files	ref	product_id	product_id	3	const	2	Using where; Using temporary; Using filesort
1	SIMPLE	cscart_product_file_descriptions	eq_ref	PRIMARY	PRIMARY	9	toolboxdigitalshop_dev.cscart_product_files.file_id,const	1	Using where

Result

file_id	product_id	file_path	preview_path	file_size	preview_size	agreement	max_downloads	total_downloads	activation_type	position	status	folder_id	file_name	license	readme
88094	46579	PCR028_1_1_We_Are_The_Resistance_(Vive_La_Frenchcore_Culemborg_Anthem_2015).mp3	PCR028_1_1_We_Are_The_Resistance_(Vive_La_Frenchcore_Culemborg_Anthem_2015)_SAMPLE.mp3	14242062	1440540	N	5	0	P	1	A		PCR028_1_1_We_Are_The_Resistance_(Vive_La_Frenchcore_Culemborg_Anthem_2015).mp3