Thanks Tutorial！
CREATE TABLE users (id INT(11) NOT NULL AUTO_INCREMENT,username VARCHAR(30) NOT NULL,pwd VARCHAR(255) NOT NULL,email VARCHAR(100) NOT NULL,createTime DATETIME NOT NULL DEFAULT CURRENT,PRIMARY KEY (id)
);CREATE TABLE comments (id INT(11) NOT NULL AUTO_INCREMENT,username VARCHAR(30) NOT NULL,commentText TEXT NOT NULL,createTime DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,userId INT(11),PRIMARY KEY (id),// FOREIGN KEY (userId) REFERENCES users (id) ON DELETE NO ACTION,// FOREIGN KEY (userId) REFERENCES users (id) ON DELETE CASCADE,FOREIGN KEY (userId) REFERENCES users (id) ON DELETE SET NULL,);INSERT INTO users (username,pwd,email) VALUES ("dingfei","733","dingfeiuniverse@gmail.com");UPDATE users SET username = 'Dxj' , pwd = '57733' WHERE username = 'DXJ' AND pwd = "577" OR username = "73341298231" ;// 可以使用 AND , OR 来连接多个条件DELETE FROM users WHERE id = 1;// 可能使 id 不从 1 开始连续，但是不要手动修改 id ，会引起外键问题SELECT username, email, createTime FROM users;// ',' 要加上不然出问题SELECT users.username FROM users;// 这也可以SELECT * FROM comments WHERE userId = 4;// * 代表所有列SELECT * FROM users INNER JOIN comments ON users.id = comments.userid;// 连接两个表的行，ON 后面是连接条件SELECT users.username, comments.commentText FROM users INNER JOIN comments ON users.id = comments.userid; // 只选择需要的列SELECT users.username, comments.commentText FROM users LEFT JOIN comments ON users.id = comments.userid; // 左连接，强制显示左表的所有行，左表若没有匹配的右表则右表显示 NULLSELECT users.username, comments.commentText FROM users RIGHT JOIN comments ON users.id = comments.userid; // 右连接，强制显示右表的所有行，右表若没有匹配的左表则左表显示 NULL// 但是在显示顺序上，左表的列还是在前面// MySQL 不支持 FULL JOIN
php 与 mysql 交互 dbh.php
<?php/* communicate to the database */$dsn = "mysql:host=localhost;dbname=hm2ns";
// dsn: data source name
$username = "root";
$password = "";
// in mac ,password is 'root';try { // 错误处理$pdo = new PDO($dsn, $username, $password);// pdo: php data object// PDO 把链接变成了一个对象，现在把一个实例化的对象赋值给 $pdo 变量$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);// 错误处理模式，设置为抛出异常} catch (PDOException $e) {// 捕获异常echo "Connection failed: " . $e->getMessage();
}
