SHOW PARTITIONS with order by in Amazon Athena - amazon-athena

Question

I have this query:
SHOW PARTITIONS tablename;
Result is:
dt=2018-01-12
dt=2018-01-20
dt=2018-05-21
dt=2018-04-07
dt=2018-01-03
This gives the list of partitions per table. The partition field for this table is dt which is a date column. I want to see the partitions ordered.
The documentation doesn't explain how to do it:
https://docs.aws.amazon.com/athena/latest/ug/show-partitions.html
I tried to add order by:
SHOW PARTITIONS tablename order by dt;
But it gives:
AmazonAthena; Status Code: 400; Error Code: InvalidRequestException;

Answer 1

AWS currently (as of Nov 2020) supports two versions of the Athena engines. How one selects and orders partitions depends upon which version is used.
Version 1:
Use the information_schema table. Assuming you have year, month as partitions (with one partition key, this is of course simpler):
WITH
a as (
SELECT partition_number as pn, partition_key as key, partition_value as val
FROM information_schema.__internal_partitions__
WHERE table_schema = 'my_database'
AND table_name = 'my_table'
)
SELECT
year, month
FROM (
SELECT val as year, pn FROM a WHERE key = 'year'
) y
JOIN (
SELECT val as month, pn FROM a WHERE key = 'month'
) m ON m.pn = y.pn
ORDER BY year, month
which outputs:
year month
0 2018 10
0 2018 11
0 2018 12
0 2019 01
...
Version 2:
Use the built-in $partitions functionality, where the partitions are explicitly available as columns and the syntax is much simpler:
SELECT year, month FROM my_database."my_table$partitions" ORDER BY year, month
year month
0 2018 10
0 2018 11
0 2018 12
0 2019 01
...
For more information, see:
https://docs.aws.amazon.com/athena/latest/ug/querying-glue-catalog.html#querying-glue-catalog-listing-partitions

Answer 2

From your comment it sounds like you're looking to sort the partitions as a way to figure out whether or not a specific partition exists. For this purpose I suggest you use the Glue API instead of querying Athena. Run aws glue get-partition help or check your preferred SDK's documentation for how it works.
There is also a variant to list all partitions of a table, run aws glue get-partitions help to read more about that. I don't think it returns the partitions in alphabetical order, but it has operators for filtering.

Answer 3

The SHOW PARTITIONS command will not allow you to order the result, since this command does not produce a resultset to sort. This command only produces a string output.
You can on the other hand query the partition column and then order the result by value.
select distinct dt from tablename order by dt asc;