php如何输出sql查询结果？

可以使用mysqli和PDO对象分别连接数据库并执行查询语句。以下是两种方法的示例代码：

使用mysqli：

<?php
//连接数据库
$db_host = "localhost";
$db_user = "root";
$db_password = "password";
$db_name = "mydb";
$conn = new mysqli($db_host, $db_user, $db_password, $db_name);

//检查连接
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

//执行查询
$sql = "SELECT * FROM mytable";
$result = $conn->query($sql);

//输出结果
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "id: " . $row["id"]. " - Name: " . $row["name"]. " - Email: " . $row["email"]. "
";
    }
} else {
    echo "0 结果";
}

//关闭连接
$conn->close();
?>

使用PDO：

<?php
//连接数据库
$db_host = "localhost";
$db_user = "root";
$db_password = "password";
$db_name = "mydb";
$dsn = "mysql:host=$db_host;dbname=$db_name";
$pdo = new PDO($dsn, $db_user, $db_password);

//执行查询
$sql = "SELECT * FROM mytable";
$stmt = $pdo->query($sql);

//输出结果
if ($stmt->rowCount() > 0) {
    while($row = $stmt->fetch()) {
        echo "id: " . $row["id"]. " - Name: " . $row["name"]. " - Email: " . $row["email"]. "
";
    }
} else {
    echo "0 结果";
}

//关闭连接
$pdo = null;
?>

注意：上述示例中使用了表名为mytable的示例表格。在实际应用中需要根据自己的情况修改数据库连接信息和查询语句。