SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    9964, 9974, 9976, 9975, 3479, 3480, 3483, 
    3486, 3494, 505, 3496, 3511, 3517, 1471, 
    1472, 1473, 1476, 3076, 3504, 3242, 
    3422, 3509, 3473, 3476, 3490, 3492, 
    3505, 3512
  )

Query time 0.00054

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "15.43"
    },
    "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": 36,
      "rows_produced_per_join": 36,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "8.24",
        "eval_cost": "7.20",
        "prefix_cost": "15.44",
        "data_read_per_join": "213K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (9964,9974,9976,9975,3479,3480,3483,3486,3494,505,3496,3511,3517,1471,1472,1473,1476,3076,3504,3242,3422,3509,3473,3476,3490,3492,3505,3512))"
    }
  }
}