SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    2930, 2935, 2942, 2948, 2957, 2970, 2975, 
    2982, 2988, 2994, 3081, 3086, 3090, 
    3098, 3106, 3117
  )

Query time 0.00032

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "9.02"
    },
    "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": 20,
      "rows_produced_per_join": 20,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "5.02",
        "eval_cost": "4.00",
        "prefix_cost": "9.02",
        "data_read_per_join": "118K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (2930,2935,2942,2948,2957,2970,2975,2982,2988,2994,3081,3086,3090,3098,3106,3117))"
    }
  }
}