This avoids having slightly different definitions of "High Value Customer" across reports.

7️⃣ View vs Table

This is an important distinction.

Table

A table physically stores data.

Customers Table → Data is stored

View

A normal View stores the query definition rather than a separate copy of the underlying data.

Customers Table → View → Query result

So if the underlying data changes, querying the View generally reflects the current underlying data.

8️⃣ View vs Temporary Table

These are also different.

View

Usually created for reusable logic:

CREATE VIEW customer_summary AS
SELECT ...

It can be used by multiple queries and users, subject to permissions.

Temporary Table

Used to store intermediate results temporarily.

For example:

CREATE TEMPORARY TABLE temp_customer_data AS
SELECT *
FROM customers
WHERE status = 'Active';

The exact temporary-table syntax varies by database.

Simple distinction:

VIEW → Reusable saved query

TEMP TABLE → Temporary stored result

9️⃣ Can You Update Data Through a View?

Sometimes.

Certain simple Views may be updatable.

For example:

CREATE VIEW active_customers AS
SELECT
    customer_id,
    customer_name,
    status
FROM customers
WHERE status = 'Active';

Depending on the database and View definition, an operation such as:

UPDATE active_customers
SET customer_name = 'New Name'
WHERE customer_id = 101;

may update the underlying table.

However, Views containing things such as:

• Aggregations

• GROUP BY

• DISTINCT

• Set operators

• Certain JOINs

• Window functions

may not be directly updatable, depending on the database.

Therefore, don't assume every View can be modified.

🔟 CREATE OR REPLACE VIEW

If your database supports it, you can modify a View definition using:

CREATE OR REPLACE VIEW active_customers AS
SELECT
    customer_id,
    customer_name,
    country,
    status
FROM customers
WHERE status = 'Active';

This allows you to change the query behind the View without creating a completely new View.

The exact syntax varies between database systems.

1️⃣1️⃣ Dropping a View

If you no longer need a View:

DROP VIEW active_customers;

This removes the View definition.

It does not normally mean that the underlying table data is deleted.

For example:

DROP VIEW customer_orders;

doesn't mean:

DELETE FROM customers;
DELETE FROM orders;

The underlying tables remain.

1️⃣2️⃣ Views for Data Security

Views can also help control which columns users can access.

Suppose your employee table contains:

employee_id

employee_name

department

salary

bank_account

You may not want every analyst to access sensitive columns.

You could create:

CREATE VIEW employee_directory AS
SELECT
    employee_id,
    employee_name,
    department
FROM employees;

Users can query:

SELECT *
FROM employee_directory;

without directly accessing columns that aren't included in the View.

Important: a View is not automatically a complete security solution. Proper database permissions are still required.

1️⃣3️⃣ Views for Business Logic

Suppose the business defines:

High Value Customer = Customer with sales >= 100,000

You can encode this definition in a View:

CREATE VIEW customer_classification AS
SELECT
    customer_id,
    customer_name,
    total_sales,
    CASE
        WHEN total_sales >= 100000
            THEN 'High Value'
        ELSE 'Standard'
    END AS customer_type
FROM customers;

Now different reports can use: