set “_rowsets_enabled”=false

By Franck Pachot

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This 12c ‘wrong results’ issue is thoroughly described by Mike Dietrich (https://blogs.oracle.com/UPGRADE/entry/switch_off_rowsets_enabled_in) and I’ve nothing to add.
This blog post is there to be used as a reference for the comment in the following recommendation that we give to our 12c customers:

alter system set "_rowsets_enabled"=false comment='see http://dbi-services.com/blog/_rowsets_enabled' scope=both;

Our best practice is to document any parameter that is set as a workaround so that it can be revert back when not needed anymore.

This post will be updated when a fix is available.
By the way, I recommend every Oracle DBA to follow Mike Dietrich blog.