A view in SQL is a virtual table created by combining data from one or more existing tables using a predefined query. Unlike physical tables, views don’t store data themselves—they dynamically display results from their underlying queries whenever they’re accessed. Views act as saved queries with names, allowing developers to simplify complex operations, enforce security by limiting column access, or present data in a specific format without altering the original tables.
To create a view, use the CREATE VIEW statement followed by a name and a SELECT query that defines the data to include. For example, if you have a customers table with columns like customer_id, name, and email, and an orders table with order_id, customer_id, and total, you could create a view to show customer names alongside their order totals. The SQL would look like this:
CREATE VIEW customer_orders AS
SELECT c.name, o.order_id, o.total
FROM customers c
JOIN orders o ON c.customer_id = o.customer_id;
This view would allow querying customer_orders as if it were a table, such as SELECT * FROM customer_orders WHERE total > 100;. Views can also include calculated fields, filters, or aggregations. For instance, a view could calculate the average order value per customer using GROUP BY.
Views are particularly useful for abstracting repetitive joins or filters, ensuring consistent logic across queries. They can also restrict access to sensitive columns (e.g., excluding email from a shared view). However, views have limitations: performance depends on the underlying query, and updating data through views may require meeting specific conditions (e.g., single-table updates without computed columns). Despite these constraints, views remain a practical tool for organizing complex SQL logic and streamlining data access.