SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    8123, 8121, 8120, 8108, 8119, 8118, 8117, 
    8116, 8115, 8114, 8112, 8111, 8110, 
    8109, 8107, 8106, 8105, 8104, 8103, 
    23780
  )

Query time 0.00034

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "4.36"
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 20,
      "rows_produced_per_join": 20,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "2.36",
        "eval_cost": "2.00",
        "prefix_cost": "4.36",
        "data_read_per_join": "51K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`maniamall_cscart`.`cscart_categories`.`parent_id` in (8123,8121,8120,8108,8119,8118,8117,8116,8115,8114,8112,8111,8110,8109,8107,8106,8105,8104,8103,23780))"
    }
  }
}