SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(306, 307, 282, 286, 291)

Query time 0.00030

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "4.70"
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "ALL",
      "possible_keys": [
        "parent"
      ],
      "rows_examined_per_scan": 40,
      "rows_produced_per_join": 20,
      "filtered": "50.00",
      "cost_info": {
        "read_cost": "2.70",
        "eval_cost": "2.00",
        "prefix_cost": "4.70",
        "data_read_per_join": "80K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`gaseus`.`cscart_categories`.`parent_id` in (306,307,282,286,291))"
    }
  }
}