SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    30421, 30427, 30423, 30426, 30430, 30414, 
    30415, 30432, 30420, 30425, 30436, 
    30439, 30434, 30441, 30443, 30417, 
    30444, 30438, 30442, 30413, 30424, 
    30446, 30419, 30437, 30416, 30447, 
    30450, 30451, 30449, 30418, 30453, 
    30428, 30452, 30454, 30455, 30431, 
    30457, 30429, 30458, 30412, 30422, 
    30435, 30433, 30448, 30456, 30440, 
    30459, 30445
  )

Query time 0.00048

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "14.77"
    },
    "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": 72,
      "rows_produced_per_join": 72,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "7.57",
        "eval_cost": "7.20",
        "prefix_cost": "14.77",
        "data_read_per_join": "186K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`maniamall_cscart`.`cscart_categories`.`parent_id` in (30421,30427,30423,30426,30430,30414,30415,30432,30420,30425,30436,30439,30434,30441,30443,30417,30444,30438,30442,30413,30424,30446,30419,30437,30416,30447,30450,30451,30449,30418,30453,30428,30452,30454,30455,30431,30457,30429,30458,30412,30422,30435,30433,30448,30456,30440,30459,30445))"
    }
  }
}

Result