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SELECT 
  thread_id, 
  type, 
  object_type, 
  object_id 
FROM 
  cscart_discussion 
WHERE 
  thread_id = 29 
  AND cscart_discussion.company_id = 1

Query time 0.00012

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	cscart_discussion	const	PRIMARY,idx_company_id	PRIMARY	3	const	1

Result

thread_id	type	object_type	object_id
29	D	C	166