SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    3402, 3403, 3404, 3390, 3391, 3405, 3406, 
    3392, 3393, 3394, 3395, 3396, 3568, 
    3397, 3407, 3398, 3577, 3570, 3580, 
    3581
  )

Query time 0.00034

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "12.23"
    },
    "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": 28,
      "rows_produced_per_join": 28,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "6.63",
        "eval_cost": "5.60",
        "prefix_cost": "12.23",
        "data_read_per_join": "166K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (3402,3403,3404,3390,3391,3405,3406,3392,3393,3394,3395,3396,3568,3397,3407,3398,3577,3570,3580,3581))"
    }
  }
}