We are using calcite to query data in Kudu. We have implemented our own
sort rule that merges rows returned from kudu when a queries orders by
columns in the same order as the primary key of the kudu table.
For a query that does a left join, in order to get the planner to use my
sort rule I had to disable the FILTER_ON_JOIN rule and use
the DUMB_FILTER_ON_JOIN (which does not try to simplify outer joins). I
also had to modify the following code in FilterJoinRule.perform()
// Try to push down above filters. These are typically where clause
// filters. They can be pushed down if they are not on the NULL
// generating side.
boolean filterPushed = false;
if (RelOptUtil.classifyFilters(
join,
aboveFilters,
joinType,
needsPushInto(join),
!joinType.generatesNullsOnLeft(),
!joinType.generatesNullsOnRight(),
joinFilters,
leftFilters,
rightFilters)) {
filterPushed = true;
}
The above code sets the pushLeft and pushRight boolean flags only if the
join type does not generate nulls on the left or right side. I was
wondering if any one knows why this is required?
If a filter only references column present in the left or right table
shouldn't we always be able to push it down?
