How do views affect performance?

Views (VIEW) don't speed anything up on their own - they don't store data, they simply run the saved query every time they're accessed.

#What to know

So from a performance standpoint:

1. Regular views (virtual views) give no speed boost - every SELECT from a VIEW runs the original SQL query again. If that query is complex (JOIN, filters, subqueries), performance suffers accordingly.
2. Materialized views are different. They store the query's result in a physical table, and the database reads already-computed data. This speeds things up at large volumes, but requires periodic refreshing (REFRESH).
3. Frequently nesting views inside other views can slow the system down, since the queries stack on top of each other.

Bottom line: views exist for convenience and logic, not optimization. To actually speed things up, use indexes, caching, or materialized VIEWs.