random memo
one of the many differences between Oracle and SQL, to be continued.
Oracle uses REDO log roll forward and uses UNDO tablespace to rollback, though theoretically can use redo(transaction log)  log to rollback but not efficient.
SQL server uses transaction log to roll forward androll back.
Noticed a good summary of Differences between UNDO and REDO in oracle by Francisco Munoz Alvarez https://oraclenz.wordpress.com/2008/06/22/differences-between-undo-and-redo/

difference of Schema:
 Schema is collection of objects, in SQL, create user doesn't create schema, in oracle then it does
in oracle a user and a schema have the same name, but SQL doesn't have to

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