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SELECT 
  cscart_attachments.*, 
  cscart_attachment_descriptions.description 
FROM 
  cscart_attachments 
  LEFT JOIN cscart_attachment_descriptions ON cscart_attachments.attachment_id = cscart_attachment_descriptions.attachment_id 
  AND lang_code = 'en' 
WHERE 
  object_type = 'product' 
  AND object_id = 672 
  AND type = 'M' 
  AND (
    usergroup_ids = '' 
    OR FIND_IN_SET(0, usergroup_ids) 
    OR FIND_IN_SET(1, usergroup_ids)
  ) 
  AND status = 'A' 
ORDER BY 
  position

Query time 0.00039

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	cscart_attachments	ref	object_type,type	object_type	95	const,const	2	Using index condition; Using where; Using filesort
1	SIMPLE	cscart_attachment_descriptions	eq_ref	PRIMARY	PRIMARY	9	mahm3t_cs443.cscart_attachments.attachment_id,const	1	Using where

Result

attachment_id	object_type	object_id	type	position	filename	filesize	usergroup_ids	status	description
96	product	672	M	0	stopter_k20_td_de.pdf	216400	0	A	(DE) Technische Daten
97	product	672	M	0	stopter_k20_td_en.pdf	327295	0	A	(EN) Technical Data