SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    841, 877, 780, 871, 759, 778, 786, 870, 
    793, 804, 760, 803, 834, 876
  )

Query time 0.00027

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_categories range parent parent 3 20 Using index condition

Result

category_id parent_id
778 759
786 759
793 759
803 759
804 759
780 760
847 834
841 834
871 870
877 876