**How to reproduce**

CH version: `20.5.2 revision 54435` (latest on `apt` at the moment). Cannot reproduce on `20.4.5`, so it's a regression.

Table:

```sql
create table repro_hits (
    date Date,
    metric Float64
) engine=MergeTree() order by date
```

Query:

```sql
SELECT
    date as period,
    1 as having_check,
    min(date) as period_start,
    addDays(max(date), 1) as period_end,
    dateDiff('second', period_start, period_end) as total_duration,
    sum(metric) as metric_
FROM repro_hits
GROUP BY period
having having_check != -1
```

**Error message and/or stacktrace**
```
Received exception from server (version 20.5.2):
Code: 179. DB::Exception: Received from localhost:9000. DB::Exception: Different expressions with the same alias period_start:
min(date) AS period_start
and
date AS period_start
.
```

The error goes away if I opt out of optimization with `SETTINGS enable_optimize_predicate_expression = 0`.
if (implicit_distinct.empty())
            return {};
    }
    
    for (const auto & id : select.select()->children)
    {
        String alias = id->tryGetAlias();
        if (const auto * identifier = id->as<ASTIdentifier>())
        {
            const String & name = identifier->shortName();
            if (select.distinct || implicit_distinct.count(name))
            {
                if (alias.empty())
                    names.insert(name);
                else
                    names.insert(alias);
            }
        }
        else if (select.distinct && !alias.empty())
        {
            
            names.insert(alias);
        }
    }
    
    if (!select.distinct && names.size() != implicit_distinct.size())
        return {};
    return names;
}
void optimizeDuplicateDistinct(ASTSelectQuery & select)