SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    9276, 6875, 2658, 266, 10511, 2653, 6340, 
    1584, 1695, 3648, 6907, 7012, 1309, 
    6328, 6473, 327, 5831
  )

Query time 0.00093

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "79.95"
    },
    "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": 197,
      "rows_produced_per_join": 197,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "40.55",
        "eval_cost": "39.40",
        "prefix_cost": "79.95",
        "data_read_per_join": "1M"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (9276,6875,2658,266,10511,2653,6340,1584,1695,3648,6907,7012,1309,6328,6473,327,5831))"
    }
  }
}