Aaaaaaron commented on a change in pull request #2253:
URL: https://github.com/apache/calcite/pull/2253#discussion_r546313841
##########
File path:
core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java
##########
@@ -366,14 +368,18 @@ public JoinReduceExpressionsRule(Class<? extends Join>
joinClass,
@Override public void onMatch(RelOptRuleCall call) {
final Join join = call.rel(0);
- final List<RexNode> expList = Lists.newArrayList(join.getCondition());
+ final RexBuilder rexBuilder = join.getCluster().getRexBuilder();
+ final RexSimplify rexSimplify =
+ new RexSimplify(rexBuilder, RelOptPredicateList.EMPTY, EXECUTOR);
+ final RexNode condition =
rexSimplify.eliminateCommonExprInCondition(join.getCondition());
+
+ final List<RexNode> expList = Lists.newArrayList(condition);
Review comment:
Hi @julianhyde
The improvement as I comment in JIRA, both have ut in this PR, this
optimization's benefit is pretty good and also it has been implemented in some
engines like spark/presto :
SQL:
```
SELECT * FROM emps,depts
WHERE
(emps.name = depts.name AND empno=1)
OR
(emps.name = depts.name AND empno=2)
```
And the join after optimizer is:
`EnumerableNestedLoopJoin(condition=[OR(AND(=($1, $11), =($0, 1)), AND(=($1,
$11), =($0, 2)))], joinType=[inner])`
In fact ($1, $11) can be extracted, and the join can be:
`HashJoin(condition=[AND(=($1, $11), OR(=($0, 1), =($0, 2)))],
joinType=[inner]) `
**We found 8 queries like this patten in TPC-DS, he benefits of optimization
are great:**
1. EnumerableNestedLoopJoin -> HashJoin
2. filter can be push down
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