Github user tejasapatil commented on the issue:
https://github.com/apache/spark/pull/16868
There are two main uses of EXTERNAL tables I am aware of:
1. Ingest data from non-hive locations into Hive tables. This can be
covered by adding test case for reading from external table creating using the
command this PR enables
2. Create a logical "pointer" to an existing hive table / partition
(without creating multiple copies of the underlying data). Testing if the
destination table can have the same location as of the source table will cover
this.
I don't think Spark's interpretation of external tables is different from
Hive's so its OK to support both.
BTW: If you are supporting 1st use case, one can mimic to get behavior of
2nd use case by creating external table with a fake location and later issuing
a `ALTER TABLE SET LOCATION` command to make it point to an existing table's
location. There is really no mechanism to guard against having EXTERNAL tables
not point to an existing table / partition in Spark. So, both use cases were
already possible in Spark
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