**Describe the bug**
Under certain conditions the equals comparison between String and Date yields the wrong result. Range Comparisons with greather-than-equals returns the correct result set.

**How to reproduce**
* Which ClickHouse server version to use: 21.2.5.5 (latest at the time of this issue)
* Which interface to use, if matters: HTTP (but should not matter)

```sql
CREATE TABLE default.myTable (
	myDay Date,
	myOrder Int32,
	someData String
) 
ENGINE = ReplacingMergeTree
PARTITION BY floor(toYYYYMMDD(myDay), -1)
ORDER BY (myOrder)
;

INSERT INTO default.myTable (myDay, myOrder) VALUES ('2021-01-01', 1);
INSERT INTO default.myTable (myDay, myOrder) VALUES ('2021-01-02', 2); // This row should be returned
INSERT INTO default.myTable (myDay, myOrder) VALUES ('2021-01-03', 3);

SELECT * FROM default.myTable mt
WHERE myDay = '2021-01-02';
```

**Expected behavior**
The last query in the example should yield the marked row. Instead it returns a empty result set.

There must be a connection to the used `PARTITION KEY`. The issue fails to reproduce as soon as I do any changes to the `PARTITION KEY` setting.

{
    RPNElement element;
    if (const auto * func = node->as<ASTFunction>())
    {
        if (tryParseLogicalOperatorFromAST(func, element))
        {
            auto & args = func->arguments->children;
            for (size_t i = 0, size = args.size(); i < size; ++i)
            {
                traverseAST(args[i], context, block_with_constants);
                /** The first part of the condition is for the correct support of `and` and `or` functions of arbitrary arity
                  * - in this case `n - 1` elements are added (where `n` is the number of arguments).
                  */
                if (i != 0 || element.function == RPNElement::FUNCTION_NOT)
                    rpn.emplace_back(element);
            }
            return;
        }
    }
    if (!tryParseAtomFromAST(node, context, block_with_constants, element))
    {
        element.function = RPNElement::FUNCTION_UNKNOWN;
    }
    rpn.emplace_back(std::move(element));
}
bool KeyCondition::canConstantBeWrappedByMonotonicFunctions(