SELECT 
  id_path 
FROM 
  categories 
WHERE 
  category_id IN (30, 212, 612, 618, 619, 620, 907, 921)

Query time 0.00430

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "3.62"
    },
    "table": {
      "table_name": "categories",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "p_category_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "category_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 8,
      "rows_produced_per_join": 8,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "2.82",
        "eval_cost": "0.80",
        "prefix_cost": "3.62",
        "data_read_per_join": "20K"
      },
      "used_columns": [
        "category_id",
        "id_path"
      ],
      "attached_condition": "(`goimagine`.`categories`.`category_id` in (30,212,612,618,619,620,907,921))"
    }
  }
}