21.5.1
```sql

create table test(d Date, k Int64, s String) 
Engine=MergeTree partition by (toYYYYMM(d),k) order by (d, k)

insert into test values ('2020-01-01', 1, '');
insert into test values ('2020-01-02', 1, '');

SELECT * FROM test WHERE d != '2020-01-01'
0 rows in set. Elapsed: 0.003 sec.


SELECT * FROM test WHERE identity(d) !=  '2020-01-01';
┌──────────d─┬─k─┬─s─┐
│ 2020-01-02 │ 1 │   │
└────────────┴───┴───┘

SELECT * FROM test WHERE toDate(d) != '2020-01-01';
┌──────────d─┬─k─┬─s─┐
│ 2020-01-02 │ 1 │   │
└────────────┴───┴───┘
```

{
    
    if (field.isExplicit())
        return applyFunctionForField(func, current_type, field);
    String result_name = "_" + func->getName() + "_" + toString(field.column_idx);
    const auto & columns = field.columns;
    size_t result_idx = columns->size();
    for (size_t i = 0; i < result_idx; ++i)
    {
        if ((*columns)[i].name == result_name)
            result_idx = i;
    }
    ColumnsWithTypeAndName args{(*columns)[field.column_idx]};
    if (result_idx == columns->size())
    {
        field.columns->emplace_back(ColumnWithTypeAndName {nullptr, func->getResultType(), result_name});
        (*columns)[result_idx].column = func->execute(args, (*columns)[result_idx].type, columns->front().column->size());
    }
    return {field.columns, field.row_idx, result_idx};
}
void KeyCondition::traverseAST(const ASTPtr & node, ContextPtr context, Block & block_with_constants)