SELECT 
  id_path 
FROM 
  cscart_categories 
WHERE 
  category_id IN (166, 186, 342, 343)

Query time 0.00032

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "p_category_id"],
      "key": "p_category_id",
      "key_length": "3",
      "used_key_parts": ["category_id"],
      "rows": 4,
      "filtered": 100,
      "index_condition": "cscart_categories.category_id in (166,186,342,343)"
    }
  }
}