问题
Is NoSQL in general, and DynamoDB in particular, well suited to performing greatest-n-per-group type queries, as compared to MySQL?
回答1:
DynamoDB support only 2 index and can only be queried efficiently on these.
- hash key
- range key (optional)
Using DynamoDB to find the biggest values in a random "row" is not a good idea at all. Querying on a random row implies scanning the whole dataset which will cost you a lot of money.
Nonetheless, if your data is properly modeled, query method may be used to find the biggest range_key for a given hash_key
Here is how to proceed:
- Set the has_key
- Set no filter for the range_key
- limit the result count to 1
- scan the index backward
来源：https://stackoverflow.com/questions/11730079/selecting-top-n-records-per-group-in-dynamodb