**Describe what's wrong**

Query with rollup using same selected field name as the name of underlying column reports structure mismatch

**Does it reproduce on recent release?**

yes

**How to reproduce**

`21.9.2.17`

```sql
CREATE TABLE test
(
    `d` DateTime,
    `a` LowCardinality(String),
    `b` UInt64
)
ENGINE = MergeTree
PARTITION BY toDate(d)
ORDER BY d;

SELECT *
FROM (
    SELECT
        a,
        max((d, b)).2 AS value
    FROM test
    GROUP BY rollup(a)
)
WHERE a <> '';
```

**Expected behavior**

This used to return an ok result on v21.8

**Error message and/or stacktrace**

> Code: 352. DB::Exception: Block structure mismatch in (columns with identical name must have identical structure) stream: different columns:
> notEquals(a, '') LowCardinality(UInt8) ColumnLowCardinality(size = 0, UInt8(size = 0), ColumnUnique(size = 1, UInt8(size = 1)))
> notEquals(a, '') LowCardinality(UInt8) Const(size = 0, ColumnLowCardinality(size = 1, UInt8(size = 1), ColumnUnique(size = 2, UInt8(size = 2)))). (AMBIGUOUS_COLUMN_NAME) (version 21.9.2.17 (official build))



&& storage->getName() != "MaterializedMySQL"
        && !row_policy_filter
        && processing_stage == QueryProcessingStage::FetchColumns
        && query_analyzer->hasAggregation()
        && (query_analyzer->aggregates().size() == 1)
        && typeid_cast<const AggregateFunctionCount *>(query_analyzer->aggregates()[0].function.get());
    if (optimize_trivial_count)
    {
        const auto & desc = query_analyzer->aggregates()[0];
        const auto & func = desc.function;
        std::optional<UInt64> num_rows{};
        if (!query.prewhere() && !query.where())
        {
            num_rows = storage->totalRows(settings);
        }
        else 
        {
            SelectQueryInfo temp_query_info;
            temp_query_info.query = query_ptr;
            temp_query_info.syntax_analyzer_result = syntax_analyzer_result;
            temp_query_info.sets = query_analyzer->getPreparedSets();
            num_rows = storage->totalRowsByPartitionPredicate(temp_query_info, context);
        }
        if (num_rows)
        {
            const AggregateFunctionCount & agg_count = static_cast<const AggregateFunctionCount &>(*func);
            
            std::vector<char> state(agg_count.sizeOfData());
            AggregateDataPtr place = state.data();
            agg_count.create(place);