Most flavors of Eclipse that I have used have shortcuts available for commenting in and out code/sql; however, it appears in HDB Studio they are not available by default.
If I have a sql editor open, go to Window → Customize Perspective → Command Groups Availability tab → Check "Java Coding" I would expect to have the shortcuts available for Toggle Comment, Add Block Comment, Remove Block Comment, and Generate Element Comment. This does seem to work in HDB Studio. Is this suppose to be a supported feature or will it become one in the near future? It would prove very useful when testing SQL.