```
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/test/java/org/elasticsearch/xpack/esql/optimizer/LogicalPlanOptimizerTests.java
assertThat(aggOne.name(), is("c"));
        var count = as(aggOne.child(), Count.class);
        var source = as(agg.child(), EsRelation.class);
    }
    /**
     * Expects
     * Limit[500[INTEGER]]
     * \_Aggregate[[],[COUNT(salary{f}#19) AS x]]
     *   \_EsRelation[test][_meta_field{f}#20, emp_no{f}#14, first_name{f}#15, ..]
     */
    public void testPruneUnusedAggMixedWithEval() {
        var plan = plan("""
              from test
            | stats c = count(salary), max = max(salary), min = min(salary)
            | eval x = c
            | keep x
            """);
        var limit = as(plan, Limit.class);
        var agg = as(limit.child(), Aggregate.class);
        assertThat(agg.groupings(), hasSize(0));
        var aggs = agg.aggregates();
        assertThat(aggs, hasSize(1));
        assertThat(Expressions.names(aggs), contains("x"));
        aggFieldName(agg.aggregates().get(0), Count.class, "salary");
        var source = as(agg.child(), EsRelation.class);
    }
    public void testPruneUnusedAggsChainedAgg() {
        var plan = plan("""
              from test
            | stats c = count(salary), max = max(salary), min = min(salary)