ESQL: Handle right hand side of Inline Stats coming optimized with LocalRelation shortcut

docs/changelog/135011.yaml

@@ -0,0 +1,6 @@
+pr: 135011
+summary: Handle right hand side of Inline Stats coming optimized with `LocalRelation`
+  shortcut
+area: ES|QL
+type: bug
+issues: []

x-pack/plugin/esql/qa/testFixtures/src/main/resources/inlinestats.csv-spec

@@ -1808,9 +1808,9 @@ from employees
 10003          |Parto          |null           |0              |null           |M              |1               |4             
 ;
 
-prunedInlinestatsFollowedByInlinestats_GroupByOneFieldOnSecondInlinestats-Ignore
-// values doesn't end up as null
+prunedInlinestatsFollowedByInlinestats_GroupByOneFieldOnSecondInlinestats
 required_capability: inline_stats
+required_capability: inline_stats_fix_pruning_null_filter
 from employees
 | eval my_length = length(concat(first_name, null))
 | inline stats count = count(my_length) where false, 
@@ -1988,9 +1988,9 @@ null             |0              |[Gino, Heping]
 null             |[0, 0, 0, 0]   |[Berni, Chirstian, Amabile, Berni, Bojan, Chirstian, Anneke, Chirstian]|[Head Human Resources, Reporting Analyst, Support Engineer, Tech Lead]|10004          
 ;
 
-prunedInlinestatsFollowedByinlinestats-Ignore
-// values doesn't end up as null
+prunedInlinestatsFollowedByInlinestats
 required_capability: inline_stats
+required_capability: inline_stats_fix_pruning_null_filter
 from employees
 | eval my_length = length(concat(first_name, null))
 | inline stats count = count(my_length) where false,

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -1528,6 +1528,12 @@ public enum Cap {
          */
         TS_COMMAND_V0(),
 
+        /**
+         * INLINE STATS fix incorrect prunning of null filtering
+         * https://github.com/elastic/elasticsearch/pull/135011
+         */
+        INLINE_STATS_FIX_PRUNING_NULL_FILTER(INLINESTATS_V11.enabled),
+
         ;
 
         private final boolean enabled;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/PruneColumns.java

@@ -24,8 +24,8 @@
 import org.elasticsearch.xpack.esql.plan.logical.LogicalPlan;
 import org.elasticsearch.xpack.esql.plan.logical.Project;
 import org.elasticsearch.xpack.esql.plan.logical.Sample;
+import org.elasticsearch.xpack.esql.plan.logical.UnaryPlan;
 import org.elasticsearch.xpack.esql.plan.logical.join.InlineJoin;
-import org.elasticsearch.xpack.esql.plan.logical.local.EmptyLocalSupplier;
 import org.elasticsearch.xpack.esql.plan.logical.local.LocalRelation;
 import org.elasticsearch.xpack.esql.plan.logical.local.LocalSupplier;
 import org.elasticsearch.xpack.esql.planner.PlannerUtils;
@@ -34,6 +34,8 @@
 import java.util.ArrayList;
 import java.util.List;
 
+import static org.elasticsearch.xpack.esql.optimizer.rules.logical.PruneEmptyPlans.skipPlan;
+
 /**
  * Remove unused columns created in the plan, in fields inside eval or aggregations inside stats.
  */
@@ -193,9 +195,9 @@ private static LogicalPlan pruneColumnsInEsRelation(EsRelation esr, AttributeSet
         return p;
     }
 
-    private static LogicalPlan emptyLocalRelation(LogicalPlan plan) {
+    private static LogicalPlan emptyLocalRelation(UnaryPlan plan) {
         // create an empty local relation with no attributes
-        return new LocalRelation(plan.source(), plan.output(), EmptyLocalSupplier.EMPTY);
+        return skipPlan(plan);
     }
 
     private static boolean isLocalEmptyRelation(LogicalPlan plan) {

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/plan/logical/join/InlineJoin.java

@@ -147,10 +147,20 @@ public static LogicalPlanTuple firstSubPlan(LogicalPlan optimizedPlan) {
         // Collect the first inlinejoin (bottom up in the tree)
         optimizedPlan.forEachUp(InlineJoin.class, ij -> {
             // extract the right side of the plan and replace its source
-            if (subPlan.get() == null && ij.right().anyMatch(p -> p instanceof StubRelation)) {
-                var p = replaceStub(ij.left(), ij.right());
-                p.setOptimized();
-                subPlan.set(new LogicalPlanTuple(p, ij.right()));
+            if (subPlan.get() == null) {
+                if (ij.right().anyMatch(p -> p instanceof StubRelation)) {
+                    var p = replaceStub(ij.left(), ij.right());
+                    p.setOptimized();
+                    subPlan.set(new LogicalPlanTuple(p, ij.right()));
+                } else if (ij.right() instanceof LocalRelation == false && ij.right().anyMatch(p -> p instanceof LocalRelation)) {
+                    // In case the plan was optimized further and the StubRelation was replaced with a LocalRelation
+                    // there is no need to replace the source of the right-hand side since it's not needed anymore
+                    // The source itself is the plan that was optimized to a LocalRelation.
+                    // This plan still needs to be executed though so that in the end is a single-node sub-tree with LocalRelation with data
+                    var p = ij.right();
+                    p.setOptimized();
+                    subPlan.set(new LogicalPlanTuple(p, ij.right()));
+                }
             }
         });
         return subPlan.get();