zabetak commented on a change in pull request #1157: [CALCITE-2969] Improve
design of join-like relational expressions
URL: https://github.com/apache/calcite/pull/1157#discussion_r279153072
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File path: core/src/main/java/org/apache/calcite/rel/core/Join.java
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@@ -230,6 +237,17 @@ public boolean isSemiJoinDone() {
return false;
}
+ /**
+ * Returns whether this LogicalJoin is a semi-join but does
+ * not comes from decorrelate.
+ *
+ * @return true if this is semi but without correlate variables.
+ */
+ public boolean isNonCorrelateSemiJoin() {
+ return (this.variablesSet == null || this.variablesSet.size() == 0)
+ && joinType == JoinRelType.SEMI;
+ }
Review comment:
Currently we have two concepts `Join` and `Correlate`. If we say that the
`Join` can have correlated variables then I don't see why we need to keep
`Correlate`.
The discussion so far (and the current PR) proposes to keep `Correlate` so
that's why I think that `Join` should not deal with correlated variables.
> Calcite supports converting from a Correlate to Join ...
@danny0405 can you explain a bit more where this is happening? I know that
the opposite is done with JoinToCorrelateRule but I don't remember seeing
CorrelateToJoinRule (or something similar). We can certainly add such a rule
but I argue that in this case we should be able to get rid of correlated
variables.
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