SELECT 
  id_path 
FROM 
  cscart_categories 
WHERE 
  category_id IN (
    1621, 1701, 1793, 1878, 1882, 1889, 1979, 
    2002
  )

Query time 0.00030

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": 8,
      "filtered": 100,
      "index_condition": "cscart_categories.category_id in (1621,1701,1793,1878,1882,1889,1979,2002)"
    }
  }
}

Result