SELECT 
  a.category_id 
FROM 
  cscart_categories as a 
  LEFT JOIN cscart_categories as b ON b.category_id IN (564) 
WHERE 
  a.id_path LIKE CONCAT(b.id_path, '/%')

Query time 0.00019

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE b const PRIMARY,p_category_id PRIMARY 3 const 1
1 SIMPLE a ALL 214 Using where

Result

category_id
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785