Unhandled Exceptions:

Remember, if it cannot search a handler for a raised exception the PL/SQL returns an unhandled exception error to the host environment that determines the outcome. For instance, in the Oracle Precompilers environment, any database modifies made through a failed SQL statement or PL/SQL block are rolled back.

Unhandled exceptions can also affect subprograms. PL/SQL assigns values to OUT parameters if you exit a subprogram successfully. Thus, PL/SQL does not assign values to OUT parameters if you exit with an unhandled exception. In addition, if a stored subprogram fails with an unhandled exception then the PL/SQL does not roll back database work done through the subprogram.

Unhandled exceptions can be prevented through coding an OTHERS handler at the topmost level of every PL/SQL block and subprogram.