SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    9365, 9540, 9541, 9538, 2856, 2888, 2775, 
    2779, 2890, 2785, 2791, 2795, 2892, 
    2894, 2895, 2908, 2909
  )

Query time 0.00051

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "11.43"
    },
    "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": 26,
      "rows_produced_per_join": 26,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "6.23",
        "eval_cost": "5.20",
        "prefix_cost": "11.43",
        "data_read_per_join": "154K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (9365,9540,9541,9538,2856,2888,2775,2779,2890,2785,2791,2795,2892,2894,2895,2908,2909))"
    }
  }
}