When computing the suppressed exceptions in ThrowableProxy, the SQLException attached exceptions could be included.

SQLException chained exceptions and java 1.7 suppressed exceptions are pretty much the same concept...

I have written a small utility that shows how this can be done:
https://github.com/zolyfarkas/spf4j/blob/master/spf4j-core/src/main/java/org/spf4j/base/Throwables.java#L274