understanding ORA-01792 maximum number of columns in a table or view is 1000

According to the My Oracle Support, ORA-01792 is caused due to an unpublished bug.

Oracle suggests to alter the query and/or view definitions to avoid the error. However in cases where the SQL cannot be adjusted then the checking can be disabled by:

SQL> alter system set "_fix_control"='17376322:OFF';

Alternatively, an interim patch(patch 19509982) can be applied to disable the error by default.

References:

Bug 19509982 Disable raising of ORA-1792 by default

Select Statement Throws ORA-01792 Error