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 │
└───────────────────────────────────────┘
```
{
        return createImpl(context.getSettingsRef().cast_keep_nullable);
    }
    static FunctionOverloadResolverImplPtr createImpl(bool keep_nullable, std::optional<Diagnostic> diagnostic = {})
    {
        return std::make_unique<CastOverloadResolver>(keep_nullable, std::move(diagnostic));
    }
    explicit CastOverloadResolver(bool keep_nullable_, std::optional<Diagnostic> diagnostic_ = {})
        : keep_nullable(keep_nullable_), diagnostic(std::move(diagnostic_))
    {}
    String getName() const override { return name; }
    size_t getNumberOfArguments() const override { return 2; }
    ColumnNumbers getArgumentsThatAreAlwaysConstant() const override { return {1}; }
protected:
    FunctionBaseImplPtr build(const ColumnsWithTypeAndName & arguments, const DataTypePtr & return_type) const override
    {
        DataTypes data_types(arguments.size());
        for (size_t i = 0; i < arguments.size(); ++i)
            data_types[i] = arguments[i].type;
        auto monotonicity = MonotonicityHelper::getMonotonicityInformation(arguments.front().type, return_type.get());
        return std::make_unique<FunctionCast>(name, std::move(monotonicity), data_types, return_type, diagnostic, cast_type);
    }
    DataTypePtr getReturnType(const ColumnsWithTypeAndName & arguments) const override