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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 = 2454 
  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 0.00051

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	1	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
2471	2454	EMP008_Ilogik_-_I_Just_Can_t_Stop_-_Technikal_vs_Fusion_DJs_Remix_-_Elasticman_Platinum.mp3	EMP008_Ilogik_-_I_Just_Can_t_Stop_-_Technikal_vs_Fusion_DJs_Remix_-_Elasticman_Platinum_SAMPLE.mp3	17511552	1440547	N	5	0	P	0	A		EMP008: Ilogik - I Just Can't Stop (Technikal vs Fusion DJ's Remix) (Elasticman Platinum)