fn column_values(
        &self,
        _column_name: &str,
        _predicate: &Predicate,
    ) -> Result<Option<StringSet>, Self::Error> {
        Ok(None)
    }
/// Return a set of Strings containing the distinct values in the
/// specified columns. If the predicate can be evaluated entirely
/// on the metadata of this Chunk. Returns `None` otherwise
///
/// The requested columns must all have String type.
Return a set of Strings containing the distinct values in the
specified columns. If the predicate can be evaluated entirely
on the metadata of this Chunk. Returns `None` otherwise

The requested columns must all have String type.
Return a set of Strings containing the distinct values in the specified columns . If the predicate can be evaluated entirely on the metadata of this Chunk . Returns ` None ` otherwise The requested columns must all have String type .
fn column_values(
        &self,
        _column_name: &str,
        _predicate: &Predicate,
    ) -> Result<Option<StringSet>, Self::Error> {
        Ok(None)
    }
fn column_values ( & self , _column_name : & str , _predicate : & Predicate , ) -> Result < Option < StringSet > , Self :: Error > { Ok ( None ) }
Return a set of Strings containing the distinct values in the
specified columns.
Return a set of Strings containing the distinct values in the specified columns .
&self
_column_name
&str
_predicate
&Predicate
&self
_column_name
&str
_predicate
&Predicate