SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    9276, 9965, 9968, 9994, 9966, 2658, 2656, 
    9986, 2853, 2760, 9977, 266, 9971, 10229, 
    9257, 2653, 2874, 932, 2793, 2695, 2724, 
    930, 9746, 9697, 2821, 2769, 2789, 2848, 
    2800, 2855, 2837, 2849
  )

Query time 0.00135

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "87.57"
    },
    "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": 216,
      "rows_produced_per_join": 216,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "44.37",
        "eval_cost": "43.20",
        "prefix_cost": "87.57",
        "data_read_per_join": "1M"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (9276,9965,9968,9994,9966,2658,2656,9986,2853,2760,9977,266,9971,10229,9257,2653,2874,932,2793,2695,2724,930,9746,9697,2821,2769,2789,2848,2800,2855,2837,2849))"
    }
  }
}