Which solution will meet this requirement?
Create a local secondary index (LSI) on the NumberOfItemsPurchased sort key.
Change the sort key from NumberOfItemsPurchased to NumberOfItemsPurchasedDescending.
In the Query operation, set the ScanIndexForward parameter to false.
In the Query operation, set the KeyConditionExpression parameter to false.
Explanations:
Creating a local secondary index (LSI) on the sort key will not change the order of the query results. An LSI allows for different sorting on the same partition key but does not modify the behavior of the original query unless explicitly used.
Changing the sort key to NumberOfItemsPurchasedDescending would not be a valid approach since DynamoDB does not support modifying existing keys directly. Instead, a new table would need to be created with the desired key structure.
Setting the ScanIndexForward parameter to false in the Query operation will sort the results in descending order based on the sort key. This is the correct method to reverse the order of results without changing the table structure.
The KeyConditionExpression parameter defines the criteria for which items to retrieve but does not control the sorting order of the results. It does not influence the sort direction like ScanIndexForward does.
I would say the answer is:
In the Query operation, set the ScanIndexForward parameter to false.