将mysqli结果转换为json

<?php
// 创建mysqli对象
$mysqli = new mysqli("localhost", "username", "password", "database");

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

// 查询语句
$sql = "SELECT id, name, age FROM users";
$result = $mysqli->query($sql);

// 创建空数组
$rows = array();

// 将结果添加到数组中
while($row = $result->fetch_assoc()) {
    $rows[] = $row;
}

// 将数组转换为json
$json_data = json_encode($rows);

// 输出json
echo $json_data;

// 关闭数据库连接
$mysqli->close();
?>