liyafan82 commented on a change in pull request #2079:
URL: https://github.com/apache/calcite/pull/2079#discussion_r460637726
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File path: core/src/main/java/org/apache/calcite/rel/rules/JoinCommuteRule.java
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@@ -59,39 +61,62 @@
@Deprecated // to be removed before 1.25
public static final JoinCommuteRule SWAP_OUTER =
CoreRules.JOIN_COMMUTE_OUTER;
+ /**
+ * This is just a sample implementation, with little practical value.
+ */
+ private static final BiPredicate<RelNode, RelNode>
DEFAULT_JOIN_CHILDREN_PREDICATE =
+ (left, right) -> left.getId() < right.getId();
+
private final boolean swapOuter;
+ private final BiPredicate<RelNode, RelNode> joinChildrenPredicate;
+
//~ Constructors -----------------------------------------------------------
/**
* Creates a JoinCommuteRule.
+ * @param clazz class for the join.
+ * @param relBuilderFactory RelNode build factory.
+ * @param swapOuter whether outer joins are supported.
+ * @param joinChildrenPredicate a predicate for the left and right children
of the join.
+ * It checks if it is of value to swap the left and right
child of the join,
+ * so the swap should happen only if the predicate yields
true.The
+ * predicate must form a partial order. That means for
different a and b,
+ * if pred(a, b) = true, then we must have pred(b, a) = false;
and vice versa.
+ * Otherwise, unexpected behaviors may occur, including endless
+ * firing of the rule.
*/
public JoinCommuteRule(Class<? extends Join> clazz,
- RelBuilderFactory relBuilderFactory, boolean swapOuter) {
+ RelBuilderFactory relBuilderFactory, boolean
swapOuter,
+ BiPredicate<RelNode, RelNode> joinChildrenPredicate) {
Review comment:
Sounds reasonable. Argument removed. Thanks.
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