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 * arg_type = named_column.type.get();
    bool ok = checkAndGetDataType<DataTypeUInt64>(arg_type)
        || checkAndGetDataType<DataTypeUInt32>(arg_type)
        || checkAndGetDataType<DataTypeUInt16>(arg_type)
        || checkAndGetDataType<DataTypeUInt8>(arg_type);
    if (!ok)
        throw Exception("Illegal type of toDecimal() scale " + named_column.type->getName(), ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
    Field field;
    named_column.column->get(0, field);
    return field.get<UInt32>();
}
struct NameToUnixTimestamp { static constexpr auto name = "toUnixTimestamp"; };
struct AccurateConvertStrategyAdditions
{
    UInt32 scale { 0 };
};
struct AccurateOrNullConvertStrategyAdditions
{