Contents

View Processing on One Page (5.2)

1. How views are processed

Approach	What it does	Pros and cons
Query modification	Rewrites a query on the view into a query on the base tables and runs that	Nothing stored, joins every time
View materialization	Builds the view as a real table and keeps it for a while	Fast, but must be updated when the base tables change (incremental update)

When a stored view is updated	When	Problem
Immediate	As soon as the base tables change	Updates even when nobody uses it
Lazy	When a query hits the view	Old values until then
Periodic	Periodically	Results may not be up to date

How many	What
2	View processing approaches
3	View update timings