SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    2900, 2899, 2898, 2897, 2896, 2895, 2894, 
    2924, 2925, 2926, 2915, 2916, 2917, 
    2918, 2919, 2920, 2921, 2922, 2923, 
    3751, 3789, 3877
  )

Query time 0.00019

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": ["parent"],
      "key": "parent",
      "key_length": "3",
      "used_key_parts": ["parent_id"],
      "rows": 22,
      "filtered": 100,
      "index_condition": "cscart_categories.parent_id in (2900,2899,2898,2897,2896,2895,2894,2924,2925,2926,2915,2916,2917,2918,2919,2920,2921,2922,2923,3751,3789,3877)"
    }
  }
}