SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    551, 512, 176, 8, 182, 23, 177, 9, 183, 
    24, 25, 184, 178, 10, 500, 179, 45, 16, 
    185, 39, 27, 28, 167, 67, 22, 180, 169, 
    431, 634, 168, 186, 187, 349, 295
  )

Query time 0.00027

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "31.46"
    },
    "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": 51,
      "rows_produced_per_join": 51,
      "filtered": "100.00",
      "index_condition": "(`dbggbern`.`cscart_categories`.`parent_id` in (551,512,176,8,182,23,177,9,183,24,25,184,178,10,500,179,45,16,185,39,27,28,167,67,22,180,169,431,634,168,186,187,349,295))",
      "cost_info": {
        "read_cost": "26.36",
        "eval_cost": "5.10",
        "prefix_cost": "31.46",
        "data_read_per_join": "204K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ]
    }
  }
}