PHP查询MYSQL，返回JSON格式？

没有接触过JSON，做一个接口时候遇到的问题，请高手指教,用PHP查询MYSQL 返回下面的参数格式{ "Msg":"success", "Contents":[ {"Name":"测试111","Url":"http://www.baidu.com/"}, {"Name":"测试222","Url":"http://www.baidu.com/"}, {"Name":"测试333","Url":"http://www.baidu.com/"} ], "Number":3, "code":0}