I use an expression as `update_field` because this feature is not implemented yet: https://github.com/ClickHouse/ClickHouse/issues/6084

20.5 generates an incorrect query in this case:
```WHERE `date_add(updated_date, interval 15 minute)` >= '2020-07-02 16:40:06'```

The exception:
```mysqlxx::BadQuery: Unknown column 'date_add(updated_date, interval 15 minute)' in 'where clause'```

The problem is here: 
https://github.com/ClickHouse/ClickHouse/blob/b81c66a03148afc02647df3c11aec40382329912/src/Dictionaries/ExternalQueryBuilder.cpp#L172
The change was introduced in this PR: https://github.com/ClickHouse/ClickHouse/pull/11079

WriteBuffer & out, size_t beg, size_t end)
{
    composeKeyTupleDefinition(out, beg, end);
    writeString(" IN (", out);
    bool first = true;
    for (const auto row : requested_rows)
    {
        if (!first)
            writeString(", ", out);
        first = false;
        composeKeyTuple(key_columns, row, out, beg, end);
    }
    writeString(")", out);
}
void ExternalQueryBuilder::composeKeyTupleDefinition(WriteBuffer & out, size_t beg, size_t end) const