SQL Views: Use Cases and Performance Tips
💡 Concept Name
SQL Views are virtual tables that store reusable SELECT query logic, allowing you to simplify and encapsulate complex SQL operations.
📘 Quick Intro
A view in SQL is not a physical table, but rather a named query stored on the server. It can be used just like a table in SELECT statements, but it fetches fresh results every time it is queried.
🧠 Analogy / Short Story
Imagine a view as a custom-made window in a building. It doesn’t store the scenery itself (data), but it gives you a curated perspective of it. You can choose what you see (columns, filters) and block out what you don’t want. SQL Views let you see just the useful parts of your data without duplicating the entire dataset.
🔧 Technical Explanation
- 🪟 A view is defined with the
CREATE VIEWstatement. - 📥 It stores a SELECT query and does not hold actual data unless indexed (materialized view).
- 🔐 Views improve security by exposing only necessary data to users.
- ♻️ Views can be queried, joined, filtered, and even updated (if the view allows).
- ⚙️ Performance depends on the underlying query, indexes, and how the view is used.
🎯 Purpose & Use Case
- ✅ Hide complex joins and subqueries for simplified access.
- ✅ Limit data access to specific columns or rows for security.
- ✅ Create a layer of abstraction between application and schema.
- ✅ Reuse query logic across multiple reports or modules.
💻 Real Code Example
-- Sample View: Top-selling products
CREATE VIEW TopSellingProducts AS
SELECT ProductName, SUM(Quantity) AS TotalSold
FROM Sales
GROUP BY ProductName
HAVING SUM(Quantity) > 100;
-- Using the view
SELECT * FROM TopSellingProducts
WHERE ProductName LIKE '%Book%';
-- Dropping the view
DROP VIEW TopSellingProducts;
❓ Interview Q&A
Q1: What is a view in SQL?
A: A view is a virtual table based on the result of a SELECT query.
Q2: Does a view store data?
A: No, it stores query logic. Results are fetched fresh on each call unless it’s a materialized view.
Q3: Can we update data using a view?
A: Yes, if the view is updatable and based on a single table without aggregates or joins.
Q4: What is the main benefit of using a view?
A: To simplify access to complex data and enforce security.
Q5: Are indexes stored on views?
A: Not on normal views, but indexed (materialized) views can store data and indexes.
Q6: Can a view be parameterized?
A: No, but you can filter it with WHERE conditions during selection.
Q7: How do views affect performance?
A: They may or may not improve performance—it depends on query complexity and indexes.
Q8: Can views include joins?
A: Yes, you can define a view over any valid SELECT, including joins and subqueries.
Q9: How to remove a view?
A: Use DROP VIEW ViewName.
Q10: Can views be nested?
A: Yes, one view can be based on another.
📝 MCQs
Q1. What does a SQL view represent?
- A stored procedure
- A backup table
- A virtual table based on a SELECT query
- An index
Q2. Which keyword is used to create a view?
- NEW VIEW
- MAKE VIEW
- CREATE VIEW
- SET VIEW
Q3. Does a normal SQL view store data?
- Yes
- No
- Sometimes
- Only with index
Q4. Which clause removes a view?
- DELETE VIEW
- REMOVE VIEW
- DROP VIEW
- TRUNCATE VIEW
Q5. What can’t a non-updatable view include?
- SELECT *
- WHERE clause
- Primary key
- Aggregate functions or joins
Q6. Can views be queried like tables?
- No
- Yes
- Only read-only
- Only with JOIN
Q7. What improves performance for complex views?
- Using aliases
- Nested views
- Indexing base tables
- Using DISTINCT
Q8. What’s a common use of views?
- Store passwords
- Export CSV
- Simplify query logic
- Optimize JOIN speed
Q9. Do views support filtering?
- No
- Yes, using WHERE
- Only in SELECT
- Only if indexed
Q10. Can views help with data security?
- No
- Yes, by limiting column access
- Only with triggers
- Only in MySQL
💡 Bonus Insight
When used well, views abstract data layers and improve maintainability. However, be cautious with performance—complex views over joins or nested queries can lead to slow execution if base tables aren't indexed or optimized.
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