PHP MySQL 读取数据
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<h2>从 MySQL 数据库读取数据</h2>
<p>SELECT 语句用于从数据表中读取数据:</p>
<pre>SELECT column_name(s) FROM table_name</pre>
<p>我们可以使用 * 号来读取所有数据表中的字段：</p>
<pre>SELECT * FROM table_name</pre>
<p>如需学习更多关于 SQL 的知识，请访问我们的 <ahref="https://www.runoob.com/sql/sql-tutorial.html">SQL 教程</a>。</p>
<hr>
<h2>使用 MySQLi</h2>
<p>以下实例中我们从 myDB 数据库的 MyGuests 表读取了 id, firstname 和 lastname 列的数据并显示在页面上：</p>
<h2>实例 (MySQLi - 面向对象)</h2>
<p><?php $servername = "localhost"; $username = "username"; $password = "password"; $dbname = "myDB"; // 创建连接 $conn = new mysqli($servername, $username, $password, $dbname); // Check connection if ($conn->connect_error) { die("连接失败: " . $conn->connect_error); } $sql = "SELECT id, firstname, lastname FROM MyGuests"; $result = $conn->query($sql); if ($result->num_rows > 0) { // 输出数据 while($row = $result->fetch_assoc()) { echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>"; } } else { echo "0 结果"; } $conn->close(); ?></p>
<p></p>
<p>以上代码解析如下:</p>
<p>首先，我们设置了 SQL 语句从 MyGuests数据表中读取 id, firstname 和 lastname 三个字段。之后我们使用该 SQL 语句从数据库中取出结果集并赋给复制给变量 $result。</p>
<p>函数 num_rows() 判断返回的数据。</p>
<p>如果返回的是多条数据，函数 fetch_assoc() 将结合集放入到关联数组并循环输出。 while() 循环出结果集，并输出 id, firstname 和 lastname 三个字段值。</p>
<p>以下实例使用 MySQLi 面向过程的方式，效果类似以上代码:</p>
<h2>实例 (MySQLi - 面向过程)</h2>
<p><?php $servername = "localhost"; $username = "username"; $password = "password"; $dbname = "myDB"; // 创建连接 $conn = mysqli_connect($servername, $username, $password, $dbname); // Check connection if (!$conn) { die("连接失败: " . mysqli_connect_error()); } $sql = "SELECT id, firstname, lastname FROM MyGuests"; $result = mysqli_query($conn, $sql); if (mysqli_num_rows($result) > 0) { // 输出数据 while($row = mysqli_fetch_assoc($result)) { echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>"; } } else { echo "0 结果"; } mysqli_close($conn); ?></p>
<p></p>
<hr>
<h2>使用 PDO (+ 预处理)</h2>
<p>以下实例使用了预处理语句。</p>
<p>选取了 MyGuests 表中的 id, firstname 和 lastname 字段，并放到 HTML 表格中：</p>
<h2>实例 (PDO)</h2>
<p><?php echo "<table style='border: solid 1px black;'>"; echo "<tr><th>Id</th><th>Firstname</th><th>Lastname</th></tr>"; class TableRows extends RecursiveIteratorIterator { function __construct($it) { parent::__construct($it, self::LEAVES_ONLY); } function current() { return "<td style='width:150px;border:1px solid black;'>" . parent::current(). "</td>"; } function beginChildren() { echo "<tr>"; } function endChildren() { echo "</tr>" . "\n"; } } $servername = "localhost"; $username = "username"; $password = "password"; $dbname = "myDBPDO"; try { $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password); $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); $stmt = $conn->prepare("SELECT id, firstname, lastname FROM MyGuests"); $stmt->execute(); // 设置结果集为关联数组 $result = $stmt->setFetchMode(PDO::FETCH_ASSOC); foreach(new TableRows(new RecursiveArrayIterator($stmt->fetchAll())) as $k=>$v) { echo $v; } } catch(PDOException $e) { echo "Error: " . $e->getMessage(); } $conn = null; echo "</table>"; ?></p>
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