SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    9435, 9434, 4926, 4948, 4965, 4986, 5049, 
    4937, 4996, 5063, 4955, 5071, 4979, 
    5078, 5007, 5081, 5019, 5027, 5037, 
    5086
  )

Query time 0.00041

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "11.03"
    },
    "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": 25,
      "rows_produced_per_join": 25,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "6.03",
        "eval_cost": "5.00",
        "prefix_cost": "11.03",
        "data_read_per_join": "148K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (9435,9434,4926,4948,4965,4986,5049,4937,4996,5063,4955,5071,4979,5078,5007,5081,5019,5027,5037,5086))"
    }
  }
}