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SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    721, 722, 723, 724, 725, 726, 727, 728, 
    729, 730, 731, 732
  ) 
  AND category_id != 264

Query time 0.00027

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		12	Using index condition; Using where