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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 = 'ru' 
WHERE 
  object_type = 'product' 
  AND object_id = 515 
  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 0.00066

JSON explain

{
  "query_block": {
    "select_id": 1,
    "const_condition": "1",
    "table": {
      "table_name": "cscart_attachments",
      "access_type": "system",
      "possible_keys": ["object_type", "type"],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "cscart_attachment_descriptions",
      "access_type": "system",
      "possible_keys": ["PRIMARY"],
      "rows": 1,
      "filtered": 100
    }
  }
}

Result

attachment_id	object_type	object_id	type	position	filename	filesize	usergroup_ids	status	description
2	product	515	M	1	Sleep_laboratory_web.pdf	40999499	0	A	Журнал "Лаборатория сна"