SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    320, 322, 321, 323, 324, 325, 326, 327, 
    328, 329, 330, 331, 332
  ) 
  AND category_id != 264

Query time 0.00033

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "23.28"
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "ALL",
      "possible_keys": [
        "PRIMARY",
        "parent",
        "p_category_id"
      ],
      "rows_examined_per_scan": 98,
      "rows_produced_per_join": 12,
      "filtered": "13.27",
      "cost_info": {
        "read_cost": "20.68",
        "eval_cost": "2.60",
        "prefix_cost": "23.28",
        "data_read_per_join": "43K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "((`danishecarter_31jan`.`cscart_categories`.`parent_id` in (320,322,321,323,324,325,326,327,328,329,330,331,332)) and (`danishecarter_31jan`.`cscart_categories`.`category_id` <> 264))"
    }
  }
}