View vs materialized view – BigQuery

In database systems, both views and materialized views are used to simplify complex queries and improve performance. However, they have significant differences in terms of how they store data and how they update it. Here’s a detailed comparison:

View

A view is a virtual table that is defined by a query. It does not store data itself but presents data from one or more tables. When you query a view, the database engine executes the underlying query to retrieve the data in real-time.

Characteristics of Views:

1. Virtual Table: A view does not store data; it dynamically fetches data from the underlying base tables.

2. Up-to-Date: Since a view retrieves real-time data from the base tables, it always shows the most current data.

3. Performance: Views do not offer performance benefits in terms of data retrieval because the underlying query is executed each time the view is accessed.

4. Use cases: Simplifying complex queries, providing a layer of abstraction, enhancing security by restricting access to certain columns or rows, and reusability of common query logic.

Example:

CREATE VIEW employee_view AS
SELECT employee_id, first_name, last_name, department
FROM employees
WHERE status = 'active';

Materialized View

A materialized view, also known as a snapshot, is a database object that contains the results of a query. Unlike a regular view, it stores data physically and needs to be refreshed to update its contents.

Characteristics of Materialized Views:

1.Physical Storage: A materialized view stores the query result set on disk, consuming storage space.

2. Performance: Since it stores data physically, querying a materialized view can be faster than querying a view, especially for complex queries or large datasets.

3. Staleness: The data in a materialized view can become stale because it is not automatically updated when the base tables change. It requires manual or scheduled refreshes.

4.Refresh Options: Materialized views can be refreshed periodically, on-demand, or automatically (depending on the database system).

5. Use Cases: Improving query performance, aggregating large datasets, and precomputing complex joins or calculations that are costly to compute on-the-fly.

Example:

CREATE MATERIALIZED VIEW employee_summary_mv AS
SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department;

Refreshing a Materialized View:

-- Manually refresh the materialized view
REFRESH MATERIALIZED VIEW employee_summary_mv;

Key Differences between view and materalized view

Conclusion

Choosing between a view and a materialized view depends on your specific requirements. Use views for dynamic, real-time data needs where up-to-date information is crucial. Use materialized views when you need to optimize query performance and can tolerate data staleness between refreshes.