SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    6580, 6711, 6574, 6760, 6590, 6729, 6667, 
    6768, 6601, 6742, 6679, 6776, 6608, 
    6685, 6785, 6614, 6699, 6791, 6618, 
    6749, 6629, 6799, 6639, 6805, 6642, 
    6813, 6658, 6820, 6824
  )

Query time 0.00062

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "18.64"
    },
    "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": 44,
      "rows_produced_per_join": 44,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "9.84",
        "eval_cost": "8.80",
        "prefix_cost": "18.64",
        "data_read_per_join": "260K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (6580,6711,6574,6760,6590,6729,6667,6768,6601,6742,6679,6776,6608,6685,6785,6614,6699,6791,6618,6749,6629,6799,6639,6805,6642,6813,6658,6820,6824))"
    }
  }
}