Method get_variable_field

datafusion/expr/src/planner.rs:126–129

Return metadata about a system/user-defined variable, if any. By default, this wraps [`Self::get_variable_type`] in an Arrow [`Field`] with nullable set to `true` and no metadata. Implementations that can provide richer information (such as nullability or extension metadata) should override this method.

(&self, variable_names: &[String])

    /// provide richer information (such as nullability or extension metadata)
    /// should override this method.
    fn get_variable_field(&self, variable_names: &[String]) -> Option<FieldRef> {
        self.get_variable_type(variable_names)
            .map(|data_type| data_type.into_nullable_field_ref())
    }

    /// Return overall configuration options
    fn options(&self) -> &ConfigOptions;