Difference between Views and Materialized Views in Postgress

Both Views and Materialized Views are powerful database objects used to simplify complex queries and manage data presentation, but they differ fundamentally in how they store and retrieve data.

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Views (Standard Views)

A standard view is a virtual table whose content is defined by a SQL query.

• Data Storage (Virtual) 👻: A view does not store data in the database. It is simply a stored query definition.
• Data Freshness (Real-time) ⏳: When you query a view, the underlying SQL is executed every time, so the data is always up-to-the-second accurate.
• Performance: Can be slower for complex queries, as the database must perform all joins and calculations each time the view is accessed.
• Use Cases:
  • Simplifying complex joins or calculations for end-users.
  • Implementing a security layer by exposing only certain columns or rows of a table.

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Materialized Views (MVs)

A materialized view is a physical table on disk that stores the results of a query, much like a cache.

• Data Storage (Physical) 💾: An MV stores a copy of the query's result set in a dedicated table structure.
• Data Freshness (Stale) 🧊: The data is not real-time. It's only as fresh as the last time the MV was refreshed.
• Performance: Queries against an MV are usually very fast because they read directly from the pre-computed table, avoiding complex runtime calculations.
• Refreshing Data: To update the data, you must manually (or scheduled) execute a REFRESH MATERIALIZED VIEW command. Until then, the data remains "stale."
• Use Cases:
  • Reporting/BI Dashboards that query complex, slow-running aggregations.
  • Creating a local copy of data from a remote server (distributed data).

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Key Differences

Feature	View (Standard)	Materialized View (MV)
Data Storage	No (Virtual Table/Stored Query)	Yes (Physical Table on disk)
Data Freshness	Always Real-Time	Stale until manually refreshed
Query Speed	Slower (query runs every time)	Faster (reads pre-calculated data)
Creation Keyword	CREATE VIEW	CREATE MATERIALIZED VIEW
Maintenance	None (always up-to-date)	Requires explicit REFRESH commands