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.

{
    
    OptimizeIfWithConstantConditionVisitor(aliases).visit(query);
    if (if_chain_to_multiif)
        OptimizeIfChainsVisitor().visit(query);
}
void TreeOptimizer::apply(ASTPtr & query, Aliases & aliases, const NameSet & source_columns_set,
                          const std::vector<TableWithColumnNamesAndTypes> & tables_with_columns,
                          const Context & context, bool & rewrite_subqueries)
{
    const auto & settings = context.getSettingsRef();
    auto * select_query = query->as<ASTSelectQuery>();
    if (!select_query)
        throw Exception("Select analyze for not select asts.", ErrorCodes::LOGICAL_ERROR);
    optimizeIf(query, aliases, settings.optimize_if_chain_to_multiif);
    
    if (settings.optimize_arithmetic_operations_in_aggregate_functions)
        optimizeAggregationFunctions(query);
    
    rewrite_subqueries = PredicateExpressionsOptimizer(context, tables_with_columns, settings).optimize(*select_query);
    
    optimizeGroupBy(select_query, source_columns_set, context);
    
    if (settings.optimize_group_by_function_keys)
        optimizeGroupByFunctionKeys(select_query);