SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    16886, 16868, 16867, 16882, 16878, 16838, 
    16856, 29953, 16904, 16863, 16894, 
    16897, 16890, 16893, 16900, 16901, 
    16898, 16902, 16892, 16895, 16840
  )

Query time 0.00033

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "4.56"
    },
    "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": 21,
      "rows_produced_per_join": 21,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "2.46",
        "eval_cost": "2.10",
        "prefix_cost": "4.56",
        "data_read_per_join": "54K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`maniamall_cscart`.`cscart_categories`.`parent_id` in (16886,16868,16867,16882,16878,16838,16856,29953,16904,16863,16894,16897,16890,16893,16900,16901,16898,16902,16892,16895,16840))"
    }
  }
}