Querying through views in SQL - Step-by-Step Execution

Concept Flow - Querying through views

Create View

↓

Store View Definition

↓

Query View

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Database Replaces View with Underlying Query

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Execute Underlying Query

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Return Result Set

A view stores a query. When you query the view, the database runs the stored query and returns its results.

Execution Sample

SQL

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

SELECT * FROM TopStudents;

Create a view named TopStudents for students scoring above 90, then query it to get those students.

Execution Table

Step	Action	Query/Condition	Result/Output
1	Create view	CREATE VIEW TopStudents AS SELECT name, score FROM Students WHERE score > 90	View TopStudents stored with query definition
2	Query view	SELECT * FROM TopStudents	Database replaces with underlying query
3	Execute underlying query	SELECT name, score FROM Students WHERE score > 90	Rows with score > 90 returned
4	Return result	N/A	[('Alice', 95), ('Bob', 92)]

💡 Query completes after returning all rows matching score > 90

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
View Definition	None	Stored as SELECT name, score FROM Students WHERE score > 90	Used to replace view in query	N/A
Query Result	None	None	[('Alice', 95), ('Bob', 92)]	[('Alice', 95), ('Bob', 92)]

Key Moments - 2 Insights

Why does querying a view run the underlying query instead of returning stored data?

The execution_table row 2 shows the database replaces the view with its stored query, so the data is fetched fresh each time.

Can the view store data like a table?

No, as shown in variable_tracker, the view only stores the query definition, not the data itself.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what query is executed?

A SELECT * FROM TopStudents

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

C SELECT name, score FROM Students WHERE score > 90

D SELECT name, score FROM Students

💡 Hint

Check execution_table row 3 under 'Query/Condition'

According to variable_tracker, what does the view store after creation?

A The actual student data

B The query definition

C Nothing

D The result set

💡 Hint

Look at 'View Definition' row after Step 2 in variable_tracker

At which step does the database replace the view with its underlying query?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

See execution_table row 2 'Action' column

Concept Snapshot

CREATE VIEW view_name AS SELECT ...;
Query the view like a table: SELECT * FROM view_name;
The database runs the stored query each time you query the view.
Views do not store data, only query definitions.
Useful for simplifying complex queries and reusing logic.

Full Transcript

A view in SQL is like a saved query. When you create a view, you store a query under a name. Later, when you query the view, the database runs the stored query and returns the results. This means views do not hold data themselves, but act like virtual tables. For example, creating a view TopStudents for students scoring above 90 lets you query TopStudents to get those students easily. The execution steps show creating the view, querying it, replacing the view with its query, running that query, and returning the results. Variables track the stored query and the result set. Common confusions include thinking views store data or that querying a view returns stored data directly. The quiz checks understanding of these steps and concepts.