[CALCITE-7514] MultiJoinOptimizeBushyRule throws AssertionError when a join condition references 3 or more factors

core/src/main/java/org/apache/calcite/rel/rules/MultiJoinOptimizeBushyRule.java

@@ -65,13 +65,9 @@
  * {@code LoptOptimizeJoinRule} is only capable of producing left-deep joins;
  * this rule is capable of producing bushy joins.
  *
- * <p>TODO:
- * <ol>
- *   <li>Join conditions that touch 1 factor.
- *   <li>Join conditions that touch 3 factors.
- *   <li>More than 1 join conditions that touch the same pair of factors,
- *       e.g. {@code t0.c1 = t1.c1 and t1.c2 = t0.c3}
- * </ol>
+ * <p>TODO: Join conditions that touch exactly 1 factor are currently applied
+ * as a filter above the join tree rather than being pushed down to the
+ * individual table scan.
  *
  * @see CoreRules#MULTI_JOIN_OPTIMIZE_BUSHY
  */
@@ -130,9 +126,17 @@ public MultiJoinOptimizeBushyRule(RelFactories.JoinFactory joinFactory,
     }
     assert x == multiJoin.getNumTotalFields();
 
+    final List<RexNode> remainingConditions = new ArrayList<>();
     final List<Edge> unusedEdges = new ArrayList<>();
     for (RexNode node : multiJoin.getJoinFilters()) {
-      unusedEdges.add(multiJoin.createEdge(node));
+      LoptMultiJoin.Edge edge = multiJoin.createEdge(node);
+      if (edge.factors.cardinality() == 2) {
+        unusedEdges.add(edge);
+      } else {
+        // Conditions touching 1 or 3+ factors cannot be used as binary join
+        // edges. Re-apply them as a filter above the finished join tree.
+        remainingConditions.add(node);
+      }
     }
 
     // Comparator that chooses the best edge. A "good edge" is one that has
@@ -170,11 +174,8 @@ private double rowCountDiff(LoptMultiJoin.Edge edge) {
       } else {
         final LoptMultiJoin.Edge bestEdge = unusedEdges.get(edgeOrdinal);
 
-        // For now, assume that the edge is between precisely two factors.
-        // 1-factor conditions have probably been pushed down,
-        // and 3-or-more-factor conditions are advanced. (TODO:)
-        // Therefore, for now, the factors that are merged are exactly the
-        // factors on this edge.
+        // Each edge in unusedEdges touches exactly two factors; conditions
+        // touching 1 or 3+ factors were separated out before the greedy loop.
         assert bestEdge.factors.cardinality() == 2;
         factors = bestEdge.factors.toArray();
       }
@@ -299,8 +300,17 @@ private double rowCountDiff(LoptMultiJoin.Edge edge) {
     }
 
     final Pair<RelNode, Mappings.TargetMapping> top = Util.last(relNodes);
-    relBuilder.push(top.left)
-        .project(relBuilder.fields(top.right));
+    relBuilder.push(top.left);
+    if (!remainingConditions.isEmpty()) {
+      final RexVisitor<RexNode> shuttle =
+          new RexPermuteInputsShuttle(top.right, top.left);
+      final List<RexNode> remapped = new ArrayList<>();
+      for (RexNode c : remainingConditions) {
+        remapped.add(c.accept(shuttle));
+      }
+      relBuilder.filter(remapped);
+    }
+    relBuilder.project(relBuilder.fields(top.right));
     call.transformTo(relBuilder.build());
   }
 

core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java

@@ -4344,6 +4344,28 @@ private void checkPushJoinThroughUnionOnRightDoesNotMatchSemiOrAntiJoin(JoinRelT
         .checkUnchanged();
   }
 
+  /** Test case for the TODO in {@link MultiJoinOptimizeBushyRule}:
+   * "Join conditions that touch 3 factors."
+   *
+   * <p>The CASE condition references three factors (e1, d, e2) and therefore
+   * cannot be represented as a binary join edge. The rule should handle it
+   * gracefully rather than throwing an {@code AssertionError}. */
+  @Test void testMultiJoinOptimizeBushyThreeFactorCondition() {
+    HepProgram preProgram = new HepProgramBuilder()
+        .addRuleInstance(CoreRules.FILTER_INTO_JOIN)
+        .addMatchOrder(HepMatchOrder.BOTTOM_UP)
+        .addRuleInstance(CoreRules.JOIN_TO_MULTI_JOIN)
+        .build();
+    HepProgram program = new HepProgramBuilder()
+        .addMatchOrder(HepMatchOrder.BOTTOM_UP)
+        .addRuleInstance(CoreRules.MULTI_JOIN_OPTIMIZE_BUSHY)
+        .build();
+    final String sql = "select e1.ename from emp e1, dept d, emp e2\n"
+        + "where e1.deptno = d.deptno and e2.deptno = d.deptno\n"
+        + "and d.deptno = case when e1.sal > 1000 then e2.empno else e1.empno end";
+    sql(sql).withPre(preProgram).withProgram(program).check();
+  }
+
   @Test void testConvertMultiJoinRule() {
     final String sql = "select e1.ename from emp e1, dept d, emp e2\n"
         + "where e1.deptno = d.deptno and d.deptno = e2.deptno";

core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml

@@ -10775,6 +10775,34 @@ LogicalAggregate(group=[{0, 1}])
   LogicalFilter(condition=[AND(=($0, 12), <>($1, 5))])
     LogicalProject(MGR=[$3], COMM=[$6])
       LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+]]>
+    </Resource>
+  </TestCase>
+  <TestCase name="testMultiJoinOptimizeBushyThreeFactorCondition">
+    <Resource name="sql">
+      <![CDATA[select e1.ename from emp e1, dept d, emp e2
+where e1.deptno = d.deptno and e2.deptno = d.deptno
+and d.deptno = case when e1.sal > 1000 then e2.empno else e1.empno end]]>
+    </Resource>
+    <Resource name="planBefore">
+      <![CDATA[
+LogicalProject(ENAME=[$1])
+  MultiJoin(joinFilter=[AND(=($18, $9), =($9, CASE(>($5, 1000), $11, $0)), =($7, $9))], isFullOuterJoin=[false], joinTypes=[[INNER, INNER, INNER]], outerJoinConditions=[[NULL, NULL, NULL]], projFields=[[ALL, ALL, ALL]])
+    LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+    LogicalTableScan(table=[[CATALOG, SALES, DEPT]])
+    LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+]]>
+    </Resource>
+    <Resource name="planAfter">
+      <![CDATA[
+LogicalProject(ENAME=[$1])
+  LogicalProject(EMPNO0=[$11], ENAME0=[$12], JOB0=[$13], MGR0=[$14], HIREDATE0=[$15], SAL0=[$16], COMM0=[$17], DEPTNO1=[$18], SLACKER0=[$19], DEPTNO=[$0], NAME=[$1], EMPNO=[$2], ENAME=[$3], JOB=[$4], MGR=[$5], HIREDATE=[$6], SAL=[$7], COMM=[$8], DEPTNO0=[$9], SLACKER=[$10])
+    LogicalFilter(condition=[=($0, CASE(>($16, 1000), $2, $11))])
+      LogicalJoin(condition=[=($18, $0)], joinType=[inner])
+        LogicalJoin(condition=[=($9, $0)], joinType=[inner])
+          LogicalTableScan(table=[[CATALOG, SALES, DEPT]])
+          LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+        LogicalTableScan(table=[[CATALOG, SALES, EMP]])
 ]]>
     </Resource>
   </TestCase>