The latest version of Amazon's SimpleDB service is available, and happily it now allows for sorting of query results. This highly-anticipated feature will make the service much more useful.
Sorting still suffers from some limitations: you can only sort by a
single attribute, you cannot perform sorting in queries that contain
union or not predicates, and the attribute against which you are
sorting must be present in a query predicate. However, it is still a
massive improvement on sorting query results in your own client code.
For example, given the following SimpleDB query that finds historic stock records for a given time period:
['Code' = 'AAPL'] intersection ['Date' > '2007-12-01']
With the new sort operator, you can now instruct the service to return
the results in reverse (descending) date order like so:
['Code' = 'AAPL'] intersection ['Date' > '2007-12-01'] sort 'Date' desc
Although you can only sort by an attribute that is also mentioned in a
predicate, you can easily work around this restriction by including a
starts-with '' predicate for that criteria, which will always evaluate
to true. Here is a query to return stock records sorted according to the
closing price, from lowest to highest:
['Code' = 'AAPL'] intersection ['Close' starts-with ''] sort 'Close' asc
The SimpleDB update also includes some other new features, such as a new
does-not-start-with operator and support for 10 predicates per query
instead of 5, but I think it is the sorting that will have the most
impact.
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