Github user wzhfy commented on the issue:
https://github.com/apache/spark/pull/16228
I still leave two issues undecided:
1. Where can we turn on/off cbo estimation? I think we need to have such
switch, because otherwise we will use statistics as long as they are in the
metastore, but they can become stale.
2. Currently we use column name as the key for column statistics, which is
problematic because if the output of join have columns from different tables
with the same column name, they can't be distinguished. Can we use a
combination string like table name + column name? Will it have problem in case
of table alias?
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