07、SQL SELECT 语句

SQL中的 SELECT 语句用于从数据库表中选取数据

 SELECT column_name, column_name FROM table_name;

或

 SELECT * FROM table_name;

SELECT 语句运行的结果会被存储在一个临时的结果表中，这个表称为结果集

演示数据

先在 MySQL 数据库运行下面的语句创建测试数据

 CREATE DATABASE IF NOT EXISTS ddkk default character set utf8mb4 collate utf8mb4_unicode_ci;

USE ddkk;

DROP TABLE IF EXISTS lession;

CREATE TABLE lession (
    id int(11) NOT NULL PRIMARY KEY AUTO_INCREMENT,
    name varchar(32) default '',
    views int(11) NOT NULL default '0',
    created_at DATETIME
);

INSERT INTO lession(id,name,views,created_at) VALUES
(1, 'Python itgogogo.cn IT gogogo',981,'2017-04-18 13:52:03'),
(2, 'Scala itgogogo.cn IT gogogo',73,'2017-04-18 16:03:32'),
(3, 'Ruby itgogogo.cn IT gogogo',199,'2017-05-01 06:16:14'),
(4, 'SQL itgogogo.cn IT gogogo', 533,'2017-05-02 08:13:42');

SELECT Column

下面的SQL 语句从 "lession" 表中选取 "name" 和 "views" 列：

 SELECT name,views FROM lession;

运行以上 SQL 语句，输出结果为:

 mysql> SELECT name,views FROM lession;
+---------------------+-------+
| name                | views |
+---------------------+-------+
| Python itgogogo.cn IT gogogo     |   981 |
| Scala itgogogo.cn IT gogogo      |    73 |
| Ruby itgogogo.cn IT gogogo       |   199 |
| SQL itgogogo.cn IT gogogo        |   533 |
+---------------------+-------+

SELECT *

下面的SQL 语句从 "lession" 表中选取所有列

 SELECT * FROM lession;

运行以上 SQL 语句，输出结果为:

 mysql> SELECT * FROM lession;
+----+---------------------+-------+---------------------+
| id | name                | views | created_at          |
+----+---------------------+-------+---------------------+
|  1 | Python itgogogo.cn IT gogogo     |   981 | 2017-04-18 13:52:03 |
|  2 | Scala itgogogo.cn IT gogogo      |    73 | 2017-04-18 16:03:32 |
|  3 | Ruby itgogogo.cn IT gogogo       |   199 | 2017-05-01 06:16:14 |
|  4 | SQL itgogogo.cn IT gogogo        |   533 | 2017-05-02 08:13:42 |
+----+---------------------+-------+---------------------+

在 SELECT 结果集中的导航

大多数数据库系统都允许使用编程函数在结果集中进行导航，比如：Move-To-First-Record、Get-Record-Content、Move-To-Next-Record 等等

类似这些编程函数不在本教程讲解之列。如需学习通过函数调用访问数据的知识，请访问我们的 PHP DDKK.COM 弟弟快看