What is a materialized view in SQL?

A materialized view in SQL is a database object that stores the result of a query as a physical table. Unlike standard views, which dynamically generate results each time they are queried, materialized views precompute and save the data, allowing for faster access at the cost of storage space. This makes them particularly useful for optimizing complex queries that are executed frequently but don’t require real-time data. For example, a materialized view might store aggregated sales data from multiple tables, reducing the need to repeatedly join large datasets during reporting.

Materialized views are most beneficial when dealing with read-heavy workloads or scenarios where query performance is critical. Since the data is precomputed, applications like dashboards, analytics tools, or batch processing systems can retrieve results instantly without recalculating joins, aggregations, or filters. However, this comes with trade-offs: the stored data becomes stale until the view is refreshed, and additional storage is required. For instance, if a materialized view aggregates daily sales, it won’t reflect new transactions until the next refresh. Developers must balance performance gains against these limitations, often scheduling refreshes during off-peak hours or using database-specific triggers to update the data.

Implementation varies across databases. In PostgreSQL, you can create a materialized view with CREATE MATERIALIZED VIEW sales_summary AS SELECT region, SUM(revenue) FROM sales GROUP BY region;. Refreshing it requires running REFRESH MATERIALIZED VIEW sales_summary;. Oracle and SQL Server offer similar functionality with automatic refresh options, such as updating the view when underlying data changes. However, not all databases support materialized views natively—MySQL, for example, requires workarounds like scheduled stored procedures to mimic the behavior. When using materialized views, consider query patterns, refresh frequency, and storage costs to determine if they align with your application’s needs.