Statistics
https://play.clickhouse.com/play?user=play#c2VsZWN0IAp0b1N0YXJ0T2ZIb3VyKGNoZWNrX3N0YXJ0X3RpbWUpIGFzIGQsCmNvdW50KCksICBncm91cFVuaXFBcnJheShwdWxsX3JlcXVlc3RfbnVtYmVyKSwgIGFueShyZXBvcnRfdXJsKQpmcm9tIGNoZWNrcyB3aGVyZSAnMjAyMi0wNi0wMScgPD0gY2hlY2tfc3RhcnRfdGltZSBhbmQgdGVzdF9uYW1lIGxpa2UgJyUwMjQ5MV9wYXJ0X2xvZ19oYXNfdGFibGVfdXVpZCUnIGFuZCB0ZXN0X3N0YXR1cyBpbiAoJ0ZBSUwnLCAnRkxBS1knKSBncm91cCBieSBkIG9yZGVyIGJ5IGQgZGVzYw==

Some times there are not output from requests.
query_info.merge_tree_empty_result = true;
        return std::nullopt;
    }
    if (selected_candidate->desc->type == ProjectionDescription::Type::Aggregate)
    {
        selected_candidate->aggregation_keys = select.getQueryAnalyzer()->aggregationKeys();
        selected_candidate->aggregate_descriptions = select.getQueryAnalyzer()->aggregates();
    }
    return *selected_candidate;
}
QueryProcessingStage::Enum MergeTreeData::getQueryProcessingStage(
    ContextPtr query_context,
    QueryProcessingStage::Enum to_stage,
    const StorageSnapshotPtr & storage_snapshot,
    SelectQueryInfo & query_info) const
{
    if (to_stage >= QueryProcessingStage::Enum::WithMergeableState)
    {
        if (auto projection = getQueryProcessingStageWithAggregateProjection(query_context, storage_snapshot, query_info))
        {
            query_info.projection = std::move(projection);
            if (query_info.projection->desc->type == ProjectionDescription::Type::Aggregate)
                return QueryProcessingStage::Enum::WithMergeableState;
        }
        else
            query_info.projection = std::nullopt;
    }
    return QueryProcessingStage::Enum::FetchColumns;
}
MergeTreeData & MergeTreeData::checkStructureAndGetMergeTreeData(IStorage & source_table, const StorageMetadataPtr & src_snapshot, const StorageMetadataPtr & my_snapshot) const