🔭 SQL VIEWS – Simplify Complex Queries with Virtual Tables
🧲 Introduction – What is a SQL VIEW?
A VIEW in SQL is a virtual table that provides a stored SQL query for simplified access to complex logic. Views do not store data themselves; they retrieve it dynamically from the underlying tables.
🎯 In this guide, you’ll learn:
- How to create, update, and use views
- The difference between views and tables
- Use cases for security, reusability, and abstraction
✅ 1. Basic CREATE VIEW Syntax
CREATE VIEW active_users AS
SELECT id, name, email
FROM users
WHERE status = 'active';
✅ You can now use SELECT * FROM active_users; just like a table.
🔁 2. Update or Replace a View
CREATE OR REPLACE VIEW active_users AS
SELECT id, name FROM users WHERE status = 'active';
✅ Updates the logic behind the view without dropping it.
❌ 3. Drop a View
DROP VIEW active_users;
✅ Removes the view definition (no data lost).
🔄 4. Read-Only vs Updatable Views
| View Type | Description |
|---|---|
| Read-only | Based on joins, aggregations, GROUP BY |
| Updatable | Simple SELECTs on a single table without joins |
⚠️ Not all views are editable. DBMS-dependent rules apply.
🔐 5. Why Use SQL Views?
| Benefit | Example Use Case |
|---|---|
| Security | Hide sensitive columns via column projection |
| Simplicity | Wrap complex joins/filters for reuse |
| Reusability | Use the same view in multiple queries/apps |
| Abstraction | Shield apps from schema changes |
📘 Best Practices
| ✅ Recommended | ❌ Avoid This |
|---|---|
Prefix views clearly (vw_ or _view) | Mixing views and tables indistinctly |
Use CREATE OR REPLACE for versioning | Dropping/recreating constantly |
| Document view logic and usage purpose | Letting unused views accumulate |
📌 Summary – Recap & Next Steps
SQL views are powerful abstractions that help simplify queries, enhance security, and promote DRY principles in data access layers.
🔍 Key Takeaways:
- Views are virtual tables that run stored SELECT queries
- Used to simplify logic, limit access, and reuse SQL patterns
- Not all views are updatable—design carefully
⚙️ Real-World Relevance:
Used in dashboards, reporting layers, role-based data access, and legacy abstraction.
➡️ Next: Explore MATERIALIZED VIEWS, indexed views, and view-based access control.
❓ FAQ – SQL VIEWS
❓ What is a SQL VIEW?
✅ A named SELECT query that behaves like a table but stores no data.
❓ Can I insert into a view?
✅ Only if the view is updatable and has no joins or aggregates.
❓ Does a view use storage space?
❌ No data is stored (unless it’s a materialized view).
❓ How do I update a view?
✅ Use CREATE OR REPLACE VIEW view_name AS ....
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