SQL Views
How to create views and interact with them in a SQL database
An interesting thing you can do with SQL is to create a view.
A view is like a table, except instead of being a real table, on its own, it is dynamically built by the result of a SELECT query.
Let’s use the example we used in the joins lesson:
CREATE TABLE people (
age INT NOT NULL,
name CHAR(20) NOT NULL PRIMARY KEY
);
CREATE TABLE cars (
brand CHAR(20) NOT NULL,
model CHAR(20) NOT NULL,
owner CHAR(20) NOT NULL PRIMARY KEY
);
We add some data:
INSERT INTO people VALUES (37, 'Flavio');
INSERT INTO people VALUES (8, 'Roger');
INSERT INTO cars VALUES ('Ford', 'Fiesta', 'Flavio');
INSERT INTO cars VALUES ('Ford', 'Mustang', 'Roger');
We can create a view that we call car_age
that always contains the correlation between a car model and its owner’s age:
CREATE VIEW car_age AS SELECT model, age AS owner_age FROM people JOIN cars ON people.name = cars.owner;
Here is the result we can inspect with SELECT * FROM car_age
:
model | owner_age
----------------------+-----------
Fiesta | 37
Mustang | 8
The view is persistent, and will look like a table in your database. You can delete a view using DROP VIEW
:
DROP VIEW car_age
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