問題：
A query operation as specified in DynamoDb documentation: DynamoDb 文檔中指定的查詢操作：
A query operation searches only primary key attribute values and supports a subset of comparison operators on key attribute values to refine the search process.查詢操作僅搜索主鍵屬性值，並支持鍵屬性值上的比較運算符子集以優化搜索過程。
and the scan operation:和掃描操作：
A scan operation scans the entire table.掃描操作掃描整個表。 You can specify filters to apply to the results to refine the values returned to you, after the complete scan.您可以指定要應用於結果的過濾器，以在完整掃描後優化返回給您的值。
Which is best based on Performance and Cost Considerations.哪個是最好的基於性能和成本考慮。