SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    2332, 2331, 2334, 2330, 2327, 2362, 2363, 
    2328, 3109, 2301, 3110, 2302, 3112, 
    3113, 1115, 2278, 2279, 2289, 2291, 
    3091
  )

Query time 0.00042

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "23.91"
    },
    "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": 42,
      "rows_produced_per_join": 42,
      "filtered": "100.00",
      "index_condition": "(`cscart_db`.`cscart_categories`.`parent_id` in (2332,2331,2334,2330,2327,2362,2363,2328,3109,2301,3110,2302,3112,3113,1115,2278,2279,2289,2291,3091))",
      "cost_info": {
        "read_cost": "19.71",
        "eval_cost": "4.20",
        "prefix_cost": "23.91",
        "data_read_per_join": "117K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ]
    }
  }
}