SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    28993, 29000, 28996, 29002, 29003, 29004, 
    29008, 28998, 30406, 29006, 29001, 
    30497, 29012, 29020, 29011, 29021, 
    29016, 29013, 29005, 28999, 30487, 
    29028, 29018, 30504, 29030, 29031, 
    29015, 30494, 29022, 29007, 30488
  )

Query time 0.00041

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "12.55"
    },
    "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": 58,
      "rows_produced_per_join": 58,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "6.75",
        "eval_cost": "5.80",
        "prefix_cost": "12.55",
        "data_read_per_join": "150K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`maniamall_cscart`.`cscart_categories`.`parent_id` in (28993,29000,28996,29002,29003,29004,29008,28998,30406,29006,29001,30497,29012,29020,29011,29021,29016,29013,29005,28999,30487,29028,29018,30504,29030,29031,29015,30494,29022,29007,30488))"
    }
  }
}

Result