SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    9477, 9476, 9489, 2922, 3020, 2958, 2917, 
    3055, 2928, 2963, 3023, 3012, 3056, 
    2964, 2934, 3016, 3027, 3057, 2941, 
    2968, 3033, 3058, 3030, 2969, 2949, 
    3043, 3059, 2954, 3044, 3060, 2973, 
    3045, 2980, 3046, 3047, 2985, 2987, 
    3048, 3049, 3001, 3008, 3050
  )

Query time 0.00052

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "28.66"
    },
    "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": 69,
      "rows_produced_per_join": 69,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "14.86",
        "eval_cost": "13.80",
        "prefix_cost": "28.66",
        "data_read_per_join": "409K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (9477,9476,9489,2922,3020,2958,2917,3055,2928,2963,3023,3012,3056,2964,2934,3016,3027,3057,2941,2968,3033,3058,3030,2969,2949,3043,3059,2954,3044,3060,2973,3045,2980,3046,3047,2985,2987,3048,3049,3001,3008,3050))"
    }
  }
}