php如何来实现返回json数据（代码）

[
    {"id":"1","address":"IANA"},
    {"id":"2","address":"美国"}
]

<?php    
header('Content-Type:application/json');  //此声明非常重要
    try {        
    $conn = new PDO("mysql:host=localhost;dbname=orig", 'admin', 'admin');        
    $conn -> setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);        
    $conn->exec("SET NAMES utf8");   //设置编码
    } catch(PDOException $e) {
        echo "conn_error:<br/>" . $e -> getMessage();
    }    $sql = "select id,address from ip_segments limit 2;";    
    $result = $conn->query($sql)->fetchAll(PDO::FETCH_ASSOC);

    echo json_encode($result,JSON_UNESCAPED_UNICODE);  //JSON_UNESCAPED_UNICODE防止中文乱码
    ?>

{
    "total":2,
    "rows":[
        {"id":"1","address":"IANA"},
        {"id":"2","address":"美国"}
    ]}

<?php
    header('Content-Type:application/json');    
    try {        
    $conn = new PDO("mysql:host=localhost;dbname=orig", 'admin', 'admin');        
    $conn -> setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);        
    $conn->exec("SET NAMES utf8");
    } catch(PDOException $e) {        
    echo "conn_error:<br/>" . $e -> getMessage();
    }    
    $sql = "select id,address from ip_segments limit 2;";    
    $result = $conn->query($sql)->fetchAll(PDO::FETCH_ASSOC);    
    $json['total'] = count($result);    
    $json['rows'] = $result;    
    echo json_encode($json,JSON_UNESCAPED_UNICODE);
    ?>