Does a view improve performance?

Views may simplify queries and improve readability, but actual performance depends on how efficiently the underlying query and base tables are indexed.

SQL Views: Use Cases and Performance Tips | FullStackPrep.Dev

Q: What is a view in SQL?

A SQL view is a virtual table created from a SELECT query. It doesn’t store data itself but lets you access filtered or joined results like a table.

💡 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 VIEW statement.
📥 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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SQL Views: Use Cases and Performance Tips