Is it possible to do something like this:

CREATE EXTERNAL TABLE T
LOCATION 's3://...'
AS
SELECT ...;

I would rather not fix the schema for T so that I can easily change the
SELECT query and its underlying tables.
Because of that, I don't want to define the table first. Instead, I have to
save the data into a temp table:

CREATE TABLE tmp AS
SELECT ...;

CREATE EXTERNAL TABLE T LIKE tmp
LOCATION 's3://...';

INSERT OVERWRITE TABLE T
SELECT * FROM tmp;

which seems to be slower than using a single INSERT with the original
SELECT.