GitHub user DaveBirdsall opened a pull request:
https://github.com/apache/incubator-trafodion/pull/1023
[TRAFODION-2552] Use column stats when SUBSTR takes a column prefix
Scenario: A join on two tables, on a column that is badly skewed in one of
the tables. The join predicate is of the form SUBSTR(skewedcolumn,1,n) =
SUBSTR(othercolumn,1,n). We use the default distribution for this predicate, so
we miss an opportunity to use skew buster.
The fix simply allows the base table column statistics to be used in this
case.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/DaveBirdsall/incubator-trafodion
SubstringStats
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/incubator-trafodion/pull/1023.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #1023
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