Remove obsolete/misleading comments in RelOptUtil#classifyFilters
The claim that filters are not pushed in the NULL generating side is not
true (at least not anymore).
Consider the following query:
SELECT *
FROM emp e
LEFT JOIN dept d
ON d.deptno > 20
In this case the filter in the ON clause can be pushed in the right
which is the NULL generating side. This is already done by the
FilterJoinRule generating a plan similar to the query below.
SELECT *
FROM emp e
LEFT JOIN (SELECT * FROM dept d WHERE d.deptno > 20) ON true
diff --git a/core/src/main/java/org/apache/calcite/plan/RelOptUtil.java b/core/src/main/java/org/apache/calcite/plan/RelOptUtil.java
index 545943b..39e55c4 100644
--- a/core/src/main/java/org/apache/calcite/plan/RelOptUtil.java
+++ b/core/src/main/java/org/apache/calcite/plan/RelOptUtil.java
@@ -2835,9 +2835,6 @@
// REVIEW - are there any expressions that need special handling
// and therefore cannot be pushed?
- // filters can be pushed to the left child if the left child
- // does not generate NULLs and the only columns referenced in
- // the filter originate from the left child
if (pushLeft && leftBitmap.contains(inputBits)) {
// ignore filters that always evaluate to true
if (!filter.isAlwaysTrue()) {
@@ -2858,18 +2855,10 @@
leftFilters.add(shiftedFilter);
}
filtersToRemove.add(filter);
-
- // filters can be pushed to the right child if the right child
- // does not generate NULLs and the only columns referenced in
- // the filter originate from the right child
} else if (pushRight && rightBitmap.contains(inputBits)) {
if (!filter.isAlwaysTrue()) {
// adjust the field references in the filter to reflect
- // that fields in the right now shift over to the left;
- // since we never push filters to a NULL generating
- // child, the types of the source should match the dest
- // so we don't need to explicitly pass the destination
- // fields to RexInputConverter
+ // that fields in the right now shift over to the left
final RexNode shiftedFilter =
shiftFilter(
nSysFields + nFieldsLeft,
