Design Pattern Que Card

This is a printable version on Design Patterns explained. A must have reference for OOP programmers.

http://www.mcdonaldland.info/2007/11/28/40/

Using Foreign Keys

This a good excerpt on usage of foreign keys in database table design.

Referential-integrity constraints are based on the concept of a foreign key. A foreign key is a column or set of columns in one table that refer to the primary key of another table. The occurrences of rows in the affected tables are governed.

Foreign keys should be used in place of application-only coded integrity checking, but it adds I/O overhead to insert and update operations.

• The additional I/O is attributable to the fact that the foreign key must be validated with the parent table. This overhead can be minimized by assuring that referenced columns are indexed.

• During bulk loads, it can be advantageous to disable integrity constraints prior to the load and re-enable the constraints after the load is completed. Once constraints are re-enabled, any errors can be noted and handled.

• One of the interesting features of referential integrity constraint is ENABLE NOVALIDATE, which can quickly create an enforced constraint, even when the constraint is believed to be true.