```
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
| enrich languages_idx on x
            | where language_name is not null
            | limit 10
            """);
        var limit = as(plan, Limit.class);
        var filter = as(limit.child(), Filter.class);
        var enrich = as(filter.child(), Enrich.class);
        assertTrue(enrich.policyName().resolved());
        assertThat(enrich.policyName().fold(), is(BytesRefs.toBytesRef("languages_idx")));
        var eval = as(enrich.child(), Eval.class);
        as(eval.child(), EsRelation.class);
    }
    /**
     * Expects
     * EsqlProject[[a{r}#3, last_name{f}#9]]
     * \_Eval[[__a_SUM_123{r}#12 / __a_COUNT_150{r}#13 AS a]]
     *   \_Limit[10000[INTEGER]]
     *     \_Aggregate[[last_name{f}#9],[SUM(salary{f}#10) AS __a_SUM_123, COUNT(salary{f}#10) AS __a_COUNT_150, last_nam
     * e{f}#9]]
     *       \_EsRelation[test][_meta_field{f}#11, emp_no{f}#5, first_name{f}#6, !g..]
     */
    public void testSimpleAvgReplacement() {
        var plan = plan("""
              from test
            | stats a = avg(salary) by last_name
            """);
        var project = as(plan, Project.class);
        assertThat(Expressions.names(project.projections()), contains("a", "last_name"));
        var eval = as(project.child(), Eval.class);
        var f = eval.fields();