SELECT 
  id_path 
FROM 
  cscart_categories 
WHERE 
  category_id IN (898, 899, 900, 974, 981, 975, 976)

Query time 0.00054

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_categories range PRIMARY,p_category_id,idx_category_id PRIMARY 3 7 Using index condition

Result

id_path
412/897/898
412/897/899
412/897/900
412/897/974
412/897/975
412/897/976
412/897/981