Retain aggregates

Author: kanoshiou

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/PruneColumns.java

@@ -10,6 +10,8 @@
 import org.elasticsearch.compute.data.Block;
 import org.elasticsearch.compute.data.BlockUtils;
 import org.elasticsearch.index.IndexMode;
+import org.elasticsearch.xpack.esql.core.expression.Alias;
+import org.elasticsearch.xpack.esql.core.expression.Attribute;
 import org.elasticsearch.xpack.esql.core.expression.AttributeSet;
 import org.elasticsearch.xpack.esql.core.expression.EmptyAttribute;
 import org.elasticsearch.xpack.esql.core.expression.Expressions;
@@ -84,7 +86,8 @@ public LogicalPlan apply(LogicalPlan plan) {
                                 );
                             } else {
                                 // Aggs cannot produce pages with 0 columns, so retain one grouping.
-                                remaining = List.of(Expressions.attribute(aggregate.groupings().get(0)));
+                                Attribute attribute = Expressions.attribute(aggregate.groupings().getFirst());
+                                remaining = aggregate.aggregates().stream().map(v -> new Alias(v.source(), v.name(), attribute)).toList();
                                 p = aggregate.with(aggregate.groupings(), remaining);
                             }
                         } else {