Friday, 15 February 2013

What is the SQL CREATE VIEW Statement Syntax and Examples

In SQL, a view is a virtual table based on the result-set of an SQL statement.
A view contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database.
You can add SQL functions, WHERE, and JOIN statements to a view and present the data as if the data were coming from one single table.


CREATE VIEW view_name AS SELECT column_name(s) FROM table_name
WHERE condition
Note: A view always shows up-to-date data! The database engine recreates the data, using the view's SQL statement, every time a user queries a view.


If you have the Northwind database you can see that it has several views installed by default.
The view "Current Product List" lists all active products (products that are not discontinued) from the "Products" table. The view is created with the following SQL:
CREATE VIEW [Current Product List] AS SELECT ProductID,ProductName
FROM Products WHERE Discontinued=No

We can query the view above as follows:

SELECT * FROM [Current Product List]

Another view in the Northwind sample database selects every product in the "Products" table with a unit price higher than the average unit price:
CREATE VIEW [Products Above Average Price] AS SELECT ProductName,UnitPrice
FROM Products WHERE UnitPrice>(SELECT AVG(UnitPrice) FROM Products)

We can query the view above as follows:
SELECT * FROM [Products Above Average Price]

Another view in the Northwind database calculates the total sale for each category in 2010. Note that this view selects its data from another view called "Product Sales for 2010":

CREATE VIEW [Category Sales For 2010] AS
SELECT DISTINCT CategoryName,Sum(ProductSales) AS CategorySales
FROM [Product Sales for 2010] GROUP BY CategoryName

We can query the view above as follows:
SELECT * FROM [Category Sales For 2010]

We can also add a condition to the query. Now we want to see the total sale only for the category "Beverages":

SELECT * FROM [Category Sales For 2010] WHERE CategoryName='Beverages'

SQL Updating a View-You can update a view by using the following syntax:

CREATE OR REPLACE VIEW view_name AS SELECT column_name(s)
FROM table_name WHERE condition

Now we want to add the "Category" column to the "Current Product List" view. We will update the view with the following SQL:

CREATE VIEW [Current Product List] AS SELECT ProductID,ProductName,Category
FROM Products WHERE Discontinued=No

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