Merge Tables

MERGE

The MERGE statement enables you to insert rows into or update rows of a table, by selecting rows from another existing table. If a row in the new data corresponds to an item that already exists in the table, then an UPDATE is performed, else an INSERT is performed.

Purpose

Use the MERGE statement to select rows from one or more sources for update or insertion into a table or view. You can specify conditions to determine whether to update or insert into the target table or view.

This statement is a convenient way to combine multiple operations. It lets you avoid multiple INSERT, UPDATE, and DELETE DML statements.

MERGE is a deterministic statement. You cannot update the same row of the target table multiple times in the same MERGE statement.

Note:

Oracle Database does not implement fine-grained access control during MERGE statements. If you are using the fine-grained access control feature on the target table or tables, then use equivalent INSERT and UPDATE statements instead of MERGE to avoid error messages and to ensure correct access control.
http://www.oracle-base.com/articles/10g/MergeEnhancements10g.php
http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/statements_9016.htm#SQLRF01606
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