Selecting top N records per group in DynamoDB

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.

1. hash key
2. 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