21.2:

```
milovidov-desktop :) SELECT CAST(1111111111.222 AS DateTime64(3))

SELECT cast(1111111111.222, 'DateTime64(3)')

Query id: d10c8623-5c74-4a38-b535-a99f6af4d28d

┌─cast(1111111111.222, 'DateTime64(3)')─┐
│               2005-03-18 04:58:31.222 │
└───────────────────────────────────────┘
```

master:

```
milovidov-desktop :) SELECT CAST(1111111111.222 AS DateTime64(3))

SELECT cast(1111111111.222, 'DateTime64(3)')

Query id: cb4af967-a4ae-4df5-89ba-234d68675f93

┌─cast(1111111111.222, 'DateTime64(3)')─┐
│               2005-03-18 04:58:31.000 │
└───────────────────────────────────────┘
```
{
        const auto & col_with_type_and_name = arguments[0];
        const IDataType & type = *col_with_type_and_name.type;
        const IColumn & col_from = *col_with_type_and_name.column;
        size_t size = col_from.size();
        auto col_to = ColumnString::create();
        ColumnString::Chars & data_to = col_to->getChars();
        ColumnString::Offsets & offsets_to = col_to->getOffsets();
        data_to.resize(size * 2); 
        offsets_to.resize(size);
        WriteBufferFromVector<ColumnString::Chars> write_buffer(data_to);
        FormatSettings format_settings;
        for (size_t i = 0; i < size; ++i)
        {
            type.serializeAsText(col_from, i, write_buffer, format_settings);
            writeChar(0, write_buffer);
            offsets_to[i] = write_buffer.count();
        }
        write_buffer.finalize();
        return col_to;
    }
};
/** Conversion of strings to numbers, dates, datetimes: through parsing.
  */
template <typename DataType>
void parseImpl(typename DataType::FieldType & x, ReadBuffer & rb, const DateLUTImpl *)