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 │   │
└────────────┴───┴───┘
```

{
    
    
    
    const ASTs & args = func->arguments->children;
    if (func->name == "not")
    {
        if (args.size() != 1)
            return false;
        out.function = RPNElement::FUNCTION_NOT;
    }
    else
    {
        if (func->name == "and" || func->name == "indexHint")
            out.function = RPNElement::FUNCTION_AND;
        else if (func->name == "or")
            out.function = RPNElement::FUNCTION_OR;
        else
            return false;
    }
    return true;
}
String KeyCondition::toString() const