自学教程WHERE 子句用于过滤记录。
WHERE 子句
WHERE 子句用于提取满足指定标准的的记录。
语法
SELECT column_name(s) FROM table_name WHERE column_name operator value
如需学习更多关于 SQL 的知识，请访问我们的 SQL 教程。
下面的实例将从 "myguests" 表中选取所有 email='john@example.com' 的行：
使用 MySQLi
MySQLi - 面向对象：
实例
<?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 WHERE email = ?";
//创建预处理语句
$stmt = $conn->prepare($sql);
$email = 'john@example.com';
//绑定参数
$stmt->bind_param("s", $email);
//执行查询
$stmt->execute();
//获取查询结果
$result = $stmt->get_result();
if ($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();
?>MySQLi - 面向过程：
实例
<?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 WHERE email = ?";
$email = 'john@example.com';
$stmt = mysqli_prepare($conn, $sql);
//绑定参数
mysqli_stmt_bind_param($stmt, "s", $email);
//执行查询
mysqli_stmt_execute($stmt);
//获取结果
$result = mysqli_stmt_get_result($stmt);
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);
?>PDO 方式
以下实例使用了预处理语句。
选取了 myguests 表中的 id, firstname 和 lastname 字段，并放到 HTML 表格中：
实例
<?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 WHERE email = :email");
$stmt->execute([':email' => 'john@example.com']);
// 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>";
?>
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