sql> alter table t modify (username not null). table altered. sql> 0select /* index(t,i_t) */ * from t. execution plan ---------------------------------------------------------- plan hash value: 3593393735 ------------------------------------------------------------------------------------ | id | operation | name | rows | bytes | cost (%cpu)| time | ------------------------------------------------------------------------------------ | 0 | 0select statement | | 27 | 918 | 2 (0)| 00:00:01 | | 1 | table access by index rowid| t | 27 | 918 | 2 (0)| 00:00:01 | | 2 | index full scan | i_t | 27 | | 1 (0)| 00:00:01 | ------------------------------------------------------------------------------------ note ----- - dynamic sampling used for this statement |