SQL视图

如何在SQL数据库中创建视图并与之交互

使用SQL可以做的一件有趣的事情是创建一个看法

视图就像一个表,只是它本身不是真正的表,而是由SELECT查询的结果动态构建的。

让我们使用在连接课程中使用的示例:

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 );

我们添加一些数据:

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');

我们可以创建一个我们称为的视图car_age始终包含汽车模型与其所有者年龄之间的相关性:

CREATE VIEW car_age AS SELECT model, age AS owner_age FROM people JOIN cars ON people.name = cars.owner;

这是我们可以检查的结果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

More database tutorials: