```
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
var a = as(aggs.get(0), Alias.class);
        assertThat(a.name(), startsWith("__a_COUNT@"));
        var sum = as(a.child(), Count.class);
        a = as(aggs.get(1), Alias.class);
        assertThat(a.name(), is("c"));
        var count = as(a.child(), Count.class);
        a = as(aggs.get(2), Alias.class);
        assertThat(a.name(), is("s"));
    }
    /**
     * Expected
     * Limit[10000[INTEGER]]
     * \_Aggregate[[last_name{f}#9],[PERCENTILE(salary{f}#10,50[INTEGER]) AS m, last_name{f}#9]]
     *   \_EsRelation[test][_meta_field{f}#11, emp_no{f}#5, first_name{f}#6, !g..]
     */
    public void testMedianReplacement() {
        var plan = plan("""
              from test
            | stats m = median(salary) by last_name
            """);
        var limit = as(plan, Limit.class);
        var agg = as(limit.child(), Aggregate.class);
        assertThat(Expressions.names(agg.aggregates()), contains("m", "last_name"));
        var aggs = agg.aggregates();
        var a = as(aggs.get(0), Alias.class);
        var per = as(a.child(), Percentile.class);
        var literal = as(per.percentile(), Literal.class);
        assertThat((int) QuantileStates.MEDIAN, is(literal.fold()));
        assertThat(Expressions.names(agg.groupings()), contains("last_name"));
    }