Hello, there. Run into the problem with DISTINCT expression. It works incorrectly on the main query if it was already applied to one of the subqueries bond with UNION ALL.

**How to reproduce**
Server version: 20.5.4.40. 19.17.6.36 was free of the bug.
Using Datagrip for running queries.
Non-default settings:
```
input_format_defaults_for_omitted_fields: 1
decimal_check_overflow: 0
joined_subquery_requires_alias: 0
```

Consider following query
```
select distinct number
from ((select number from numbers(10)) union all (select number from numbers(20)));
```
It works fine, returning 20 rows as expected.

But if we add distinct to subqueries (it doesn't matter to the first, the second or both)
```
select distinct number
from ((select distinct number from numbers(10)) union all (select distinct number from numbers(20)));
```

Then in 20.5.4.40 we'll see 30 rows with numbers from 0 to 9 duplicated.
However, `count(distinct number)` returns the correct number of rows.

{
    GroupByKeysInfo data;
    
    for (auto & group_key : group_keys)
    {
        if (group_key->as<ASTFunction>())
            data.has_function = true;
        if (auto * group_key_ident = group_key->as<ASTIdentifier>())
        {
            data.has_identifier = true;
            if (data.key_names.count(group_key_ident->shortName()))
            {
                
                
                
                data.has_possible_collision = true;
            }
            data.key_names.insert(group_key_ident->shortName());
        }