```
show functions | rename synopsis AS foo | stats bar = count(*) by foo | drop foo
```

```
{
    "error": {
        "root_cause": [
            {
                "type": "null_pointer_exception",
                "reason": "Cannot invoke \"org.elasticsearch.xpack.ql.expression.Attribute.id()\" because \"sourceAttribute\" is null"
            }
        ],
        "type": "null_pointer_exception",
        "reason": "Cannot invoke \"org.elasticsearch.xpack.ql.expression.Attribute.id()\" because \"sourceAttribute\" is null"
    },
    "status": 500
}
```

```
[2023-11-14T09:49:51,479][WARN ][r.suppressed             ] [runTask-0] path: /_query, params: {format=txt}, status: 500 java.lang.NullPointerException: Cannot invoke "org.elasticsearch.xpack.ql.expression.Attribute.id()" because "sourceAttribute" is null
        at org.elasticsearch.xpack.esql.planner.EsPhysicalOperationProviders.ordinalGroupingOperatorFactory(EsPhysicalOperationProviders.java:172)
        at org.elasticsearch.xpack.esql.planner.AbstractPhysicalOperationProviders.groupingPhysicalOperation(AbstractPhysicalOperationProviders.java:148)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planAggregation(LocalExecutionPlanner.java:234)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:182)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planAggregation(LocalExecutionPlanner.java:233)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:182)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planProject(LocalExecutionPlanner.java:571)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:196)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planLimit(LocalExecutionPlanner.java:610)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:200)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planOutput(LocalExecutionPlanner.java:310)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:224)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:168)
        at org.elasticsearch.xpack.esql.plugin.ComputeService.runCompute(ComputeService.java:260)
```
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/LogicalPlanOptimizer.java
new PushDownRegexExtract(),
            new PushDownEnrich(),
            new PushDownAndCombineOrderBy(),
            new PruneOrderByBeforeStats(),
            new PruneRedundantSortClauses()
        );
        var skip = new Batch<>("Skip Compute", new SkipQueryOnLimitZero());
        var cleanup = new Batch<>("Clean Up", new ReplaceLimitAndSortAsTopN());
        var defaultTopN = new Batch<>("Add default TopN", new AddDefaultTopN());
        var label = new Batch<>("Set as Optimized", Limiter.ONCE, new SetAsOptimized());
        return asList(substitutions, operators, skip, cleanup, defaultTopN, label);
    }
    
    static class SubstituteSurrogates extends OptimizerRules.OptimizerRule<Aggregate> {
        SubstituteSurrogates() {
            super(TransformDirection.UP);
        }
        @Override
        protected LogicalPlan rule(Aggregate aggregate) {
            var aggs = aggregate.aggregates();
            List<NamedExpression> newAggs = new ArrayList<>(aggs.size());
            
            Map<AggregateFunction, Attribute> aggFuncToAttr = new HashMap<>();
            
            List<Alias> transientEval = new ArrayList<>();
            boolean changed = false;
            
            for (NamedExpression agg : aggs) {
                if (agg instanceof Alias a && a.child() instanceof AggregateFunction af && af instanceof SurrogateExpression == false) {
                    aggFuncToAttr.put(af, a.toAttribute());