NOTE
DDL can be performed on a global temporary table as long as there are
no sessions currently inserting rows into the global temporary table.
There are a few other things to keep in mind when using temporary tables. Although you can
create an index on a temporary table, the entries in the index are dropped along with the data
rows, as with a regular table. Also, due to the temporary nature of the data in a temporary table,
no recovery-related redo information is generated for DML on temporary tables; however, undo
information is created in the undo tablespace and redo information to protect the undo. If all you
do is insert and select from your global temporary tables, very little redo is generated. Because the
table definition itself is not temporary, it persists between sessions until it is explicitly dropped.
External Tables
Sometimes you want to access data that resides outside of the database in a text format, but
|you want to use it as if it were a table in the database. Although you could use a utility such as
SQL*Loader to load the table into the database, the data may be quite volatile or your user base??™s
expertise might not include executing SQL*Loader at the Windows or Unix command line.
To address these needs, you can use external tables, which are read-only tables whose
definition is stored within the database but whose data stays external to the database. There are a
few drawbacks to using external tables: You cannot index external tables, and you cannot execute
update, insert, and delete statements against an external table.
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