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Oracle Tips by Burleson |
OCP Instructors Guide for
Oracle DBA Certification
Chapter 8 -
Miscellaneous Oracle Information
Unindexed Foreign Keys
and Locking Problems
The referential integrity relationship is established by creating a
foreign key constraint on a table that points to or “references” the
primary or unique key constraint in another table. The foreign key
constraint declaration consists of: a constraint name (optional),
the columns comprising the foreign key, a clause that references the
table containing the primary or unique key constraint and a delete
clause (discussed later).
The table being referenced by the foreign key
is called the parent table while the table containing the foreign
key is called the child or dependent table. The foreign key columns
must match the primary key or unique key columns in number and
should match the primary key or unique key column’s datatypes and
column lengths.
The following business rules are established
when the foreign key is created:
-
When inserting a row into the dependent table,
Oracle identifies the contents of the foreign key columns and checks
to see if a matching value exists in the parent table’s primary key
or unique key columns. If a matching value is not found in the
parent table, the insert is rejected.
-
When the columns comprising the foreign key are
updated, Oracle performs the same check as when rows are being
inserted.
-
Deleting rows in the dependent table is
permitted.
The above text is
an excerpt from:
OCP Instructors Guide for Oracle DBA Certification
A Study Guide to Advanced Oracle Certified Professional Database
Administration Techniques
ISBN 0-9744355-3-8
by Christopher T. Foot
http://www.rampant-books.com/book_2003_2_OCP_print.htm
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