Oracle
12c has increased the maximum length of character-based columns to 32K bytes -
don't get too excited, they're stored out of lines (so similar in cost to LOBs)
and need some modification to the parameter file and data dictionary (starting
the database in upgrade mode) before you can use them.


Richard
Foote has a pair of articles on indexing such columns:





Be
cautious about enabling this option and test carefully - there are going to be a
number of side effects, and some of them may require a significant investment in
time to resolve. The first one that came to my mind was that if you've created a
function-based index on a pl/sql function that returns a varchar2() type and
haven't explicitly created the index on a substr() of the return value then the
data type of the function's return value will change from the current default of
varchar2(4000) to varchar2(32767) - which means the index will become invalid
and can't be rebuilt or recreated.


Obviously
you can redefine the index to include an explicit substr() call - but then you
have to find all the code that was supposed to use the index and modify it
accordingly.




转自joanthan levis