We foolishly moved to 12c with optimizer_adaptive_features enabled. It broke a lot of things & the side effects lasted long beyond turning it off, a warning to those still on 11g.
One of the problems was we could not modify a column from char to varchar2(larger) when there was data in the table. The first time this happened we fixed it by removing everything from dba_stat_extensions.
This time though a new database was left with optimizer_adaptive_features enabled by mistake & now the same problem occurs. But this time removing from dba_stat_extensions isn't fixing it & the extra step from here isn't doing the job either: Completely Disabling Adaptive Query Optimization in Oracle Database 12c - Oracle Wiki - Oracle - Toad World
Any of you experienced similar in 12c? What other things could be preventing the modification?
alter table x modify (ID VARCHAR2(12 CHAR)) -- from IDÂ CHAR(9 CHAR)