View as a saved query mental model in SQL - Step-by-Step Execution

Concept Flow - View as a saved query mental model

Write SELECT query

↓

Create View with query

↓

View stores query as saved object

↓

Use View in SELECT like a table

↓

Database runs saved query and returns results

You write a SELECT query and save it as a view. Later, you query the view like a table, and the database runs the saved query to give results.

Execution Sample

SQL

CREATE VIEW TopStudents AS
SELECT name, score FROM Students WHERE score > 90;

SELECT * FROM TopStudents;

Create a view named TopStudents that saves a query for students scoring above 90, then select all from that view.

Execution Table

Step	Action	Query/Command	Result/Effect
1	Create view	CREATE VIEW TopStudents AS SELECT name, score FROM Students WHERE score > 90;	View 'TopStudents' saved with query
2	Query view	SELECT * FROM TopStudents;	Database runs saved query and returns rows with score > 90
3	Return results	N/A	Rows of students with score above 90 displayed

💡 View acts as stored query; querying it runs the saved SELECT and returns results.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
TopStudents (view)	Not defined	Defined as SELECT name, score FROM Students WHERE score > 90	Used to run saved query	Returns filtered student rows

Key Moments - 2 Insights

Is the data stored inside the view itself?

No, the view only stores the query, not the data. When you query the view (see execution_table step 2), the database runs the saved query on the actual data.

Can I use a view like a regular table in SELECT statements?

Yes, as shown in execution_table step 2, you can SELECT from the view just like a table, and it returns the query results.

Visual Quiz - 3 Questions

Look at the execution_table, what happens at step 1?

A The view is created and saved with a query

B The view data is displayed

C The view is deleted

D The database updates the Students table

💡 Hint

Refer to execution_table row 1 under 'Result/Effect'

At which step does the database run the saved query inside the view?

A Step 1

B Step 2

C Step 3

D Never

💡 Hint

See execution_table step 2 'Database runs saved query...'

If the Students table changes after creating the view, what will the view show when queried?

A No data at all

B Old data from when view was created

C Updated data based on current Students table

D An error

💡 Hint

Views run the saved query on current data, see concept_flow last step

Concept Snapshot

CREATE VIEW view_name AS SELECT ...;
- View stores a SELECT query, not data.
- Query the view like a table: SELECT * FROM view_name;
- View runs saved query on current data each time.
- Useful for reusing complex queries easily.

Full Transcript

A view in SQL is like a saved SELECT query. You create it with CREATE VIEW and a SELECT statement. The view itself does not store data but remembers the query. When you SELECT from the view, the database runs the saved query on the current data and returns the results. This lets you reuse complex queries easily by just querying the view as if it were a table.

Practice

1. What is a SQL view best described as?

easy

A. A backup copy of a database

B. A physical table storing data permanently

C. A saved query that acts like a virtual table

D. A user account with special permissions

Solution

1. Step 1: Understand what a view is

   A view is not a physical table but a saved SQL query that can be treated like a table.

2. Step 2: Compare options to definition

   A saved query that acts like a virtual table matches the definition exactly. The other options describe different database concepts like backups, physical tables, or user permissions.

3. Final Answer:

   A saved query that acts like a virtual table -> Option C

4. Quick Check:

   View = saved query acting like table [OK]

Hint: Remember: Views are saved queries, not real tables [OK]

Common Mistakes:

• Thinking views store data physically
• Confusing views with backups
• Assuming views are user accounts

2. Which of the following is the correct syntax to create a view named EmployeeView showing all columns from Employees table?

easy

A. VIEW CREATE EmployeeView SELECT * FROM Employees;

B. CREATE TABLE EmployeeView AS SELECT * FROM Employees;

C. SELECT * INTO EmployeeView FROM Employees;

D. CREATE VIEW EmployeeView AS SELECT * FROM Employees;

Solution

1. Step 1: Recall the syntax for creating a view

   The correct syntax starts with CREATE VIEW, followed by the view name, AS, then the SELECT query.

2. Step 2: Check each option

   CREATE VIEW EmployeeView AS SELECT * FROM Employees; matches the correct syntax. CREATE TABLE EmployeeView AS SELECT * FROM Employees; creates a table, not a view. SELECT * INTO EmployeeView FROM Employees; is for SELECT INTO which creates a table. VIEW CREATE EmployeeView SELECT * FROM Employees; is invalid syntax.

3. Final Answer:

   CREATE VIEW EmployeeView AS SELECT * FROM Employees; -> Option D

4. Quick Check:

   CREATE VIEW ... AS SELECT ... [OK]

Hint: Use CREATE VIEW ... AS SELECT ... to define views [OK]

Common Mistakes:

• Using CREATE TABLE instead of CREATE VIEW
• Confusing SELECT INTO with view creation
• Incorrect keyword order in syntax

3. Given the table Products with columns id, name, and price, and the view created as:
CREATE VIEW CheapProducts AS SELECT id, name FROM Products WHERE price < 50;
What will the query SELECT * FROM CheapProducts; return if Products contains:

id | name    | price
1  | Pen     | 10
2  | Notebook| 60
3  | Eraser  | 30

medium

A. Rows with id 1, 2, and 3 showing all columns

B. Rows with id 1 and 3 showing id and name columns

C. Rows with id 2 only showing id and name columns

D. No rows returned because price is not selected

Solution

1. Step 1: Understand the view definition

   The view selects id and name from Products where price is less than 50.

2. Step 2: Apply the filter to the data

   Products with price less than 50 are id 1 (price 10) and id 3 (price 30). The view returns only id and name columns.

3. Final Answer:

   Rows with id 1 and 3 showing id and name columns -> Option B

4. Quick Check:

   View filters price < 50 and selects id, name [OK]

Hint: View returns filtered columns and rows as defined [OK]

Common Mistakes:

• Expecting all columns in view output
• Including rows that don't meet WHERE condition
• Thinking view stores data separately

4. You created a view with:
CREATE VIEW ActiveUsers AS SELECT id, name FROM Users WHERE active = 1;
But running SELECT * FROM ActiveUsers; gives an error: ERROR: relation "activeusers" does not exist
What is the most likely cause?

medium

A. The view was not created successfully or was dropped

B. The SELECT query inside the view has syntax errors

C. The Users table does not have an 'active' column

D. You must refresh the view before selecting from it

Solution

1. Step 1: Analyze the error message

   The error says the relation (view) "activeusers" does not exist, meaning the view is missing.

2. Step 2: Consider causes for missing view

   This usually means the view was never created or was dropped. Syntax errors or missing columns cause errors during creation, not this runtime error. Views do not require refreshing.

3. Final Answer:

   The view was not created successfully or was dropped -> Option A

4. Quick Check:

   Missing view = creation failed or dropped [OK]

Hint: Check if view exists before querying it [OK]

Common Mistakes:

• Assuming syntax errors cause this runtime error
• Thinking views need refreshing like materialized views
• Ignoring case sensitivity or schema issues

5. You want to create a view RecentOrders that always shows orders placed in the last 7 days from the Orders table with columns order_id, customer_id, and order_date. Which SQL statement correctly creates this view?

hard

A. CREATE VIEW RecentOrders AS SELECT order_id, customer_id, order_date FROM Orders WHERE order_date > CURRENT_DATE - INTERVAL '7 days';

B. CREATE VIEW RecentOrders AS SELECT order_id, customer_id FROM Orders WHERE order_date > CURRENT_DATE - INTERVAL '7 days';

C. CREATE VIEW RecentOrders AS SELECT * FROM Orders WHERE order_date > DATEADD(day, -7, GETDATE());

D. CREATE VIEW RecentOrders AS SELECT order_id, customer_id FROM Orders WHERE order_date > SYSDATE - 7;

Solution

1. Step 1: Identify needed columns and date filter

   The view should include order_id, customer_id, and order_date columns and filter orders from last 7 days.

2. Step 2: Check each option's correctness

   CREATE VIEW RecentOrders AS SELECT order_id, customer_id FROM Orders WHERE order_date > CURRENT_DATE - INTERVAL '7 days'; misses order_date column, so it won't show the date. CREATE VIEW RecentOrders AS SELECT order_id, customer_id, order_date FROM Orders WHERE order_date > CURRENT_DATE - INTERVAL '7 days'; includes all needed columns and uses correct standard SQL interval syntax. CREATE VIEW RecentOrders AS SELECT * FROM Orders WHERE order_date > DATEADD(day, -7, GETDATE()); uses SQL Server syntax (DATEADD, GETDATE) which may not be standard. CREATE VIEW RecentOrders AS SELECT order_id, customer_id FROM Orders WHERE order_date > SYSDATE - 7; uses SYSDATE which is Oracle-specific and may not work in standard SQL.

3. Final Answer:

   CREATE VIEW RecentOrders AS SELECT order_id, customer_id, order_date FROM Orders WHERE order_date > CURRENT_DATE - INTERVAL '7 days'; -> Option A

4. Quick Check:

   Include needed columns and use standard interval syntax [OK]

Hint: Include all needed columns and use standard date intervals [OK]

Common Mistakes:

• Omitting important columns in view
• Using non-standard date functions
• Forgetting to filter by date correctly