$sql = "SELECT a FROM `table_a`";
首先檢測搜索得到的字符串的編碼類型
mb_detect_encoding($row['a'], array("ASCII",'UTF-8',"GB2312","GBK",'BIG5'));
如果得到的編碼類型不是"UTF-8",則無法使用json_decode進行編碼。
當編碼爲"ASCII",轉換成"UTF-8":
iconv('ASCII','UTF-8',$row['a']);
當編碼爲"GB2312"/"GBK",轉換成"UTF-8":
urlencode(iconv('ASCII','UTF-8',$row['a']));
再使用json_encode