A nonunique index can be used to enforce a primary key or unique constraint. In Oracle8i indexes can be rebuilt without locking the table. The DROP COLUMN option of the ALTER TABLE command is restartable. The MOVE option of the ALTER TABLE command retains the constraints of the table. Data rows in the global temporary table are always deleted when A user session is terminated 1.
本文转自maclean_007 51CTO博客，原文链接:http://blog.51cto.com/maclean/1276702
