SELECT 
  id_path 
FROM 
  cscart_categories 
WHERE 
  category_id IN (
    1, 18, 20, 26, 46, 54, 57, 67, 70, 82, 85, 
    107, 114, 237, 240, 241, 243, 257, 261, 
    306
  )

Query time 0.00045

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["category_id"],
      "rows": 20,
      "filtered": 100,
      "index_condition": "cscart_categories.category_id in (1,18,20,26,46,54,57,67,70,82,85,107,114,237,240,241,243,257,261,306)"
    }
  }
}