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 DataTypes & argument_types_, const DataTypePtr & return_type_
        , std::optional<Diagnostic> diagnostic_, CastType cast_type_)
        : name(name_), monotonicity_for_range(std::move(monotonicity_for_range_))
        , argument_types(argument_types_), return_type(return_type_), diagnostic(std::move(diagnostic_))
        , cast_type(cast_type_)
    {
    }
    const DataTypes & getArgumentTypes() const override { return argument_types; }
    const DataTypePtr & getResultType() const override { return return_type; }
    ExecutableFunctionImplPtr prepare(const ColumnsWithTypeAndName & ) const override
    {
        try
        {
            return std::make_unique<ExecutableFunctionCast>(
                    prepareUnpackDictionaries(getArgumentTypes()[0], getResultType()), name, diagnostic);
        }
        catch (Exception & e)
        {
            if (diagnostic)
                e.addMessage("while converting source column " + backQuoteIfNeed(diagnostic->column_from) +
                             " to destination column " + backQuoteIfNeed(diagnostic->column_to));
            throw;
        }
    }
    String getName() const override { return name; }