The CC BY-SA license is incompatible with the ODbL license.
The confusing thing about ODbL is that it seems to pertain to entire databases, rather than to individual works.
Is it possible then to have a database that contains both ODbL data as well as CC BY-SA data?
If not, do I understand correctly that this can be worked around by having two wholly separate databases, one per license, and simply combining the content from both databases on the front-end? (The ODbL license states that "A work that constitutes a Collective Database will not be considered a Derivative Database," so I assume so.)