Querying for greatest value of Range key on AWS DynamoDb

boto amazon-dynamodb
Vishal picture Vishal · Aug 23, 2014 · Viewed 26.7k times · Source

What is the DynamoDB equivalent of

SELECT MAX(RANGE_KEY) FROM MYTABLE WHERE PRIMARYKEY = "value"

The best I can come up with is

from boto.dynamodb2.table import Table as awsTable

tb = awsTable("MYTABLE")
rs = list(tb.query_2(PRIMARYKEY__eq="value", reverse=True, limit=1))
MAXVALUE = rs[0][RANGE_KEY]

Is there a better way to do this?

Answer

bsd picture bsd · Apr 1, 2015

That's the correct way.

Because the records matched by the Hash Key are sorted by the Range Key, getting the first one by the descendant order will give you the record with the maximum range key.

Query results are always sorted by the range key. If the data type of the range key is Number, the results are returned in numeric order; otherwise, the results are returned in order of ASCII character code values. By default, the sort order is ascending. To reverse the order use the ScanIndexForward parameter set to false.

Query and Scan Operations - Amazon DynamoDB : http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/QueryAndScan.html

NOTE: Setting the reverse parameter to true via boto API is equivalent to setting ScanIndexForward to false via the native AWS API.

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