Sandbox

SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    734, 735, 736, 737, 738, 739, 740, 741, 
    742, 743, 744, 745, 746, 747, 748
  ) 
  AND category_id != 264

Query time 0.00035

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	cscart_categories	range	PRIMARY,parent,p_category_id	parent	3		15	Using index condition; Using where