SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    9965, 9968, 9980, 9967, 2658, 2656, 2721, 
    2797, 2853, 2760, 2761, 2804
  )

Query time 0.00074

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "53.50"
    },
    "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": 131,
      "rows_produced_per_join": 131,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "27.31",
        "eval_cost": "26.20",
        "prefix_cost": "53.51",
        "data_read_per_join": "776K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (9965,9968,9980,9967,2658,2656,2721,2797,2853,2760,2761,2804))"
    }
  }
}