[fix](nereids)PushDownJoinOnAssertNumRows rule process project alias bug

fe/fe-core/src/main/java/org/apache/doris/nereids/rules/analysis/CheckAfterRewrite.java

@@ -94,6 +94,18 @@ private void checkUnexpectedExpression(Plan plan) {
         }
     }
 
+    /**
+     *
+     * used for test
+     * after applying a rule, use this method to check whether all slots are from children
+     */
+    public void checkTreeAllSlotReferenceFromChildren(Plan plan) {
+        checkAllSlotReferenceFromChildren(plan);
+        for (Plan child : plan.children()) {
+            checkTreeAllSlotReferenceFromChildren(child);
+        }
+    }
+
     private void checkAllSlotReferenceFromChildren(Plan plan) {
         Set<Slot> inputSlots = plan.getInputSlots();
         RoaringBitmap childrenOutput = plan.getChildrenOutputExprIdBitSet();

fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/PushDownJoinOnAssertNumRows.java

@@ -216,8 +216,21 @@ private Plan pushDownAssertNumRowsJoin(LogicalJoin topJoin) {
 
     @VisibleForTesting
     LogicalProject<? extends Plan> projectAliasOnPlan(List<Alias> projections, Plan child) {
-        List<NamedExpression> newProjections = Lists.newArrayList(child.getOutput());
-        newProjections.addAll(projections);
-        return new LogicalProject<>(newProjections, child);
+        if (child instanceof LogicalProject) {
+            LogicalProject<? extends Plan> project = (LogicalProject<? extends Plan>) child;
+            List<NamedExpression> newProjections =
+                    Lists.newArrayList(project.getProjects());
+            for (Alias alias : projections) {
+                if (!project.getOutput().contains(alias.toSlot())) {
+                    NamedExpression expr = (NamedExpression) project.pushDownExpressionPastProject(alias);
+                    newProjections.add(expr);
+                }
+            }
+            return project.withProjects(newProjections);
+        } else {
+            List<NamedExpression> newProjections = Lists.newArrayList(child.getOutput());
+            newProjections.addAll(projections);
+            return new LogicalProject<>(newProjections, child);
+        }
     }
 }

fe/fe-core/src/test/java/org/apache/doris/nereids/rules/rewrite/PushDownJoinOnAssertNumRowsTest.java

@@ -470,7 +470,6 @@ void testProjectAliasOnPlan() {
         Assertions.assertTrue(newPlan instanceof LogicalProject
                 && newPlan.getOutput().size() == 2
                 && ((LogicalProject<?>) newPlan).getOutputs().get(0).equals(slot)
-                && ((LogicalProject<?>) newPlan).getOutputs().get(1).equals(alias)
-                && newPlan.child(0) instanceof LogicalProject);
+                && ((LogicalProject<?>) newPlan).getOutputs().get(1).equals(alias));
     }
 }