CTAS with location clause acts as an insert overwrite. This can cause problems when there sub directories with in a directory.
This cause some users accidentally wipe out directories with very important data. We should ban CTAS with location to a non-empty directory.
create table ctas1
select * from jsmall limit 10;
create table ctas2
select * from jsmall limit 5;
Both creates will succeed. But value in table ctas1 will be replaced by ctas2 accidentally.