This is perhaps the second most advanced expertise I have, though again I didn't do much formal training on this except a query developer course on TSQL. What I can do includes:

• Datatbase design in MS SQL or MySQL (MyISAM or InnoDB) with appropriate schemas and enforcement of data model (as much as it is possible in MyISAM though)
• Query design, query performance review, indexing strategies
• Complex query design in MS SQL (aggregate functions, windowing, pivoting) 
• Development of SQL routines for triggers and functions
• Geospatial column management
• Understanding of ArcGIS data model in SQL Express (ArcGIS-workgroup...)
• Some expertise with open source ones like H2, Postgres, Java DB/Derby
• SQL Azure and some MySQL on Appengine
• MS Access/Jet
• ...and so on...