SELECT 
  id_path 
FROM 
  cscart_categories 
WHERE 
  category_id IN (
    267, 271, 276, 278, 288, 294, 297, 300, 
    323
  )

Query time 0.00027

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "6.31"
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "p_category_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "category_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 9,
      "rows_produced_per_join": 9,
      "filtered": "100.00",
      "index_condition": "(`wearethehelpful_scalesta_net`.`cscart_categories`.`category_id` in (267,271,276,278,288,294,297,300,323))",
      "cost_info": {
        "read_cost": "5.41",
        "eval_cost": "0.90",
        "prefix_cost": "6.31",
        "data_read_per_join": "23K"
      },
      "used_columns": [
        "category_id",
        "id_path"
      ]
    }
  }
}