apache · iwanttobepowerful · Jan 23, 2026
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/SubQueryRemoveRule.java b/core/src/main/java/org/apache/calcite/rel/rules/SubQueryRemoveRule.java
@@ -884,6 +884,7 @@ private static List<RexNode> fields(RelBuilder builder, int fieldCount) {
   private static void matchProject(SubQueryRemoveRule rule,
       RelOptRuleCall call) {
     final Project project = call.rel(0);
+    final Set<CorrelationId> projectVariablesSet = project.getVariablesSet();
     final RelBuilder builder = call.builder();
     final RexSubQuery e =
         requireNonNull(RexUtil.SubQueryFinder.find(project.getProjects()));
@@ -894,6 +895,10 @@ private static void matchProject(SubQueryRemoveRule rule,
     final int fieldCount = builder.peek().getRowType().getFieldCount();
     final Set<CorrelationId>  variablesSet =
         RelOptUtil.getVariablesUsed(e.rel);
+    if (!projectVariablesSet.isEmpty()) {
+      // Only consider the correlated variables which originated from this sub-query level.
+      variablesSet.retainAll(projectVariablesSet);
+    }
     final RexNode target =
         rule.apply(e, variablesSet, logic, builder, 1, fieldCount, 0);
     final RexShuttle shuttle = new ReplaceSubQueryShuttle(e, target);

diff --git a/core/src/test/java/org/apache/calcite/sql2rel/RelDecorrelatorTest.java b/core/src/test/java/org/apache/calcite/sql2rel/RelDecorrelatorTest.java
@@ -208,6 +208,101 @@ public static Frameworks.ConfigBuilder config() {
     assertThat(after, hasTree(planAfter));
   }
 
+  /** Test case for <a href="https://issues.apache.org/jira/browse/CALCITE-7057">[CALCITE-7057]
+   * NPE when decorrelating query containing nested correlated subqueries</a>. */
+  @Test void test7057() {
+    final FrameworkConfig frameworkConfig = config().build();
+    final RelBuilder builder = RelBuilder.create(frameworkConfig);
+    final RelOptCluster cluster = builder.getCluster();
+    final Planner planner = Frameworks.getPlanner(frameworkConfig);
+    final String sql = ""
+        + "select\n"
+        + " (select ename || ' from dept '\n"
+        + " || (select dname from dept where deptno = emp.deptno and emp.empno = empnos.empno)\n"
+        + "       from emp\n"
+        + "    ) as ename_from_dept\n"
+        + "from (values (7369), (7499)) as empnos(empno) order by 1";
+    final RelNode originalRel;
+    try {
+      final SqlNode parse = planner.parse(sql);
+      final SqlNode validate = planner.validate(parse);
+      originalRel = planner.rel(validate).rel;
+    } catch (Exception e) {
+      throw TestUtil.rethrow(e);
+    }
+
+    final HepProgram hepProgram = HepProgram.builder()
+        .addRuleCollection(
+            ImmutableList.of(
+                // SubQuery program rules
+                CoreRules.FILTER_SUB_QUERY_TO_CORRELATE,
+                CoreRules.PROJECT_SUB_QUERY_TO_CORRELATE,
+                CoreRules.JOIN_SUB_QUERY_TO_CORRELATE))
+        .build();
+    final Program program =
+        Programs.of(hepProgram, true,
+            requireNonNull(cluster.getMetadataProvider()));
+    final RelNode before =
+        program.run(cluster.getPlanner(), originalRel, cluster.traitSet(),
+            Collections.emptyList(), Collections.emptyList());
+
+    // before fix:
+    //
+    // LogicalSort(sort0=[$0], dir0=[ASC])
+    //  LogicalProject(ENAME_FROM_DEPT=[$1])
+    //    LogicalCorrelate(correlation=[$cor2], joinType=[left], requiredColumns=[{0}])
+    //      LogicalValues(tuples=[[{ 7369 }, { 7499 }]])
+    //      LogicalAggregate(group=[{}], agg#0=[SINGLE_VALUE($0)])
+    //        LogicalProject(EXPR$0=[||(||($1, ' from dept '), $8)])
+    //          LogicalJoin(condition=[true], joinType=[left], variablesSet=[[$cor0, $cor2]])
+    //            LogicalTableScan(table=[[scott, EMP]])
+    //            LogicalAggregate(group=[{}], agg#0=[SINGLE_VALUE($0)])
+    //              LogicalProject(DNAME=[$1])
+    //                LogicalFilter(condition=[AND(=($0, $cor0.DEPTNO),
+    //                              =(CAST($cor0.EMPNO):INTEGER NOT NULL, $cor2.EMPNO))])
+    //                  LogicalTableScan(table=[[scott, DEPT]])
+    //
+    final String planBefore = ""
+        + "LogicalSort(sort0=[$0], dir0=[ASC])\n"
+        + "  LogicalProject(ENAME_FROM_DEPT=[$1])\n"
+        + "    LogicalCorrelate(correlation=[$cor2], joinType=[left], requiredColumns=[{0}])\n"
+        + "      LogicalValues(tuples=[[{ 7369 }, { 7499 }]])\n"
+        + "      LogicalAggregate(group=[{}], agg#0=[SINGLE_VALUE($0)])\n"
+        + "        LogicalProject(EXPR$0=[||(||($1, ' from dept '), $8)])\n"
+        + "          LogicalCorrelate(correlation=[$cor0], joinType=[left], requiredColumns=[{0, 7}])\n"
+        + "            LogicalTableScan(table=[[scott, EMP]])\n"
+        + "            LogicalAggregate(group=[{}], agg#0=[SINGLE_VALUE($0)])\n"
+        + "              LogicalProject(DNAME=[$1])\n"
+        + "                LogicalFilter(condition=[AND(=($0, $cor0.DEPTNO), =(CAST($cor0.EMPNO):INTEGER NOT NULL, $cor2.EMPNO))])\n"
+        + "                  LogicalTableScan(table=[[scott, DEPT]])\n";
+    assertThat(before, hasTree(planBefore));
+
+    // Decorrelate without any rules, just "purely" decorrelation algorithm on RelDecorrelator
+    final RelNode after =
+        RelDecorrelator.decorrelateQuery(before, builder, RuleSets.ofList(Collections.emptyList()),
+            RuleSets.ofList(Collections.emptyList()));
+    final String planAfter = ""
+        + "LogicalSort(sort0=[$0], dir0=[ASC])\n"
+        + "  LogicalProject(ENAME_FROM_DEPT=[$2])\n"
+        + "    LogicalJoin(condition=[IS NOT DISTINCT FROM($0, $1)], joinType=[left])\n"
+        + "      LogicalValues(tuples=[[{ 7369 }, { 7499 }]])\n"
+        + "      LogicalAggregate(group=[{0}], agg#0=[SINGLE_VALUE($1)])\n"
+        + "        LogicalProject(EMPNO1=[$12], EXPR$0=[||(||($1, ' from dept '), $13)])\n"
+        + "          LogicalJoin(condition=[AND(=($7, $10), =($9, $11))], joinType=[left])\n"
+        + "            LogicalProject(EMPNO=[$0], ENAME=[$1], JOB=[$2], MGR=[$3], HIREDATE=[$4], SAL=[$5], COMM=[$6], DEPTNO=[$7], DEPTNO0=[$7], EMPNO0=[CAST($0):INTEGER NOT NULL])\n"
+        + "              LogicalTableScan(table=[[scott, EMP]])\n"
+        + "            LogicalAggregate(group=[{0, 1, 2}], agg#0=[SINGLE_VALUE($3)])\n"
+        + "              LogicalProject(DEPTNO0=[$3], EMPNO0=[$4], EMPNO=[$5], DNAME=[$1])\n"
+        + "                LogicalJoin(condition=[=($0, $3)], joinType=[inner])\n"
+        + "                  LogicalTableScan(table=[[scott, DEPT]])\n"
+        + "                  LogicalJoin(condition=[=($1, $2)], joinType=[inner])\n"
+        + "                    LogicalAggregate(group=[{0, 1}])\n"
+        + "                      LogicalProject(DEPTNO=[$7], EMPNO0=[CAST($0):INTEGER NOT NULL])\n"
+        + "                        LogicalTableScan(table=[[scott, EMP]])\n"
+        + "                    LogicalValues(tuples=[[{ 7369 }, { 7499 }]])\n";
+    assertThat(after, hasTree(planAfter));
+  }
+
   @Test void testDecorrelateCountBug() {
     final FrameworkConfig frameworkConfig = config().build();
     final RelBuilder builder = RelBuilder.create(frameworkConfig);

diff --git a/core/src/test/resources/sql/scalar.iq b/core/src/test/resources/sql/scalar.iq
@@ -451,4 +451,14 @@ EnumerableCalc(expr#0..10=[{inputs}], EMPNO=[$t0], $f1=[$t10])
 # Reset to default value true
 !set trimfields true
 
+# [CALCITE-7057] NPE when decorrelating query containing nested correlated subqueries
+# Nested scalar sub-queries
+select
+    (select ename || ' from dept '
+                  || (select dname from dept where deptno = emp.deptno and emp.empno = empnos.empno)
+       from emp
+    ) as ename_from_dept
+from (values (7369), (7499)) as empnos(empno) order by 1;
+more than one value in agg SINGLE_VALUE
+!error
 # End scalar.iq