When people were handling duplicated entry error from DB, sometimes
they were trying to find out the specific columns where the value is
duplicated. However, such information are not in the exception object
which is inconvenient. People were even trying to do another query to
find out the duplicated columns. This patch addresses it.
Change-Id: If3ebcdfb5c3a5ddba1e2ebb6cb0ff79239e1ccd3