danny0405 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_r276599667
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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:
In the beginning, i add this method to distinguish the `SemiJoin`
transformed from `Correlate` and `SemiJoin` from `SemiJoinRule` or
`RelBuilder`. Cause i thought that the join comes from a `Correlate` can make a
JoinRelType.SEMI join type.
But in current code, Calcite will never transform from Correlate to join
with `JoinRelType.SEMI`(only left and inner join type), so this method actually
can simplify to just decide if the join type is `JoinRelType.SEMI`.
But i still keep the variables check and i think correlate should have the
ability to get a semi join type join.
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