Sandbox

SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(777, 775, 792, 801, 815, 755, 819)

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	cscart_categories	range	parent	parent	3		13	Using index condition