**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.

out_key_column_num = it->second;
                out_key_column_type = sample_block.getByName(it->first).type;
                return true;
            }
        }
    }
    return false;
}
bool KeyCondition::tryPrepareSetIndex(
    const ASTs & args,
    ContextPtr context,
    RPNElement & out,
    size_t & out_key_column_num)
{
    const ASTPtr & left_arg = args[0];
    out_key_column_num = 0;
    std::vector<MergeTreeSetIndex::KeyTuplePositionMapping> indexes_mapping;
    DataTypes data_types;
    auto get_key_tuple_position_mapping = [&](const ASTPtr & node, size_t tuple_index)
    {
        MergeTreeSetIndex::KeyTuplePositionMapping index_mapping;
        index_mapping.tuple_index = tuple_index;
        DataTypePtr data_type;
        if (isKeyPossiblyWrappedByMonotonicFunctions(
                node, context, index_mapping.key_index, data_type, index_mapping.functions))
        {
            indexes_mapping.push_back(index_mapping);
            data_types.push_back(data_type);
            if (out_key_column_num < index_mapping.key_index)
                out_key_column_num = index_mapping.key_index;