```
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
var aliases = aliasBuilder.build();
            var expressionsWithResolvedAliases = (UnaryPlan) parent.transformExpressionsOnly(
                ReferenceAttribute.class,
                r -> aliases.resolve(r, r)
            );
            return project.replaceChild(expressionsWithResolvedAliases.replaceChild(project.child()));
        } else {
            throw new EsqlIllegalArgumentException("Expected child to be instance of Project");
        }
    }
    /**
     * Combine disjunctions on the same field into an In expression.
     * This rule looks for both simple equalities:
     * 1. a == 1 OR a == 2 becomes a IN (1, 2)
     * and combinations of In
     * 2. a == 1 OR a IN (2) becomes a IN (1, 2)
     * 3. a IN (1) OR a IN (2) becomes a IN (1, 2)
     *
     * This rule does NOT check for type compatibility as that phase has been
     * already be verified in the analyzer.
     */
    public static class CombineDisjunctionsToIn extends OptimizerRules.CombineDisjunctionsToIn {
        protected In createIn(Expression key, List<Expression> values, ZoneId zoneId) {
            return new In(key.source(), key, values);
        }
        protected Equals createEquals(Expression k, Set<Expression> v, ZoneId finalZoneId) {
            return new Equals(k.source(), k, v.iterator().next(), finalZoneId);
        }
    }
    static class ReplaceLimitAndSortAsTopN extends OptimizerRules.OptimizerRule<Limit> {