如何调试为什么最简单的MySQL查询返回false? [英] How can I debug why simplest MySQL query returns false?
问题描述
我与xampp合作.我执行了MySQL连接:
I work with xampp. I performed MySQL connection:
$connection = mysql_connect($host , $user , $passw);
mysql_select_db($db, $connection);
我通过echo命令(通过检查布尔返回值)接收到输出，该连接已建立并且已找到数据库$ db.
I received output with echo command (by check the boolean returned values) that connection is established and the database $db is found.
但最简单的查询如下:
$query = mysql_query("SELECT * FROM 'users'");
返回假.我该如何调试原因?
returns false. How can I debug why?Thanks.
推荐答案
强制性更新:由于mysql ext不再存在，以下是我在我的网站上基于剩下的两个MySQL API的答案回答关于堆栈溢出的上千个问题的经验:
An obligatory update: as mysql ext is no more, here are answers for two remaining MySQL APIs which I written on my site based on the experience from answering 1000s questions on Stack Overflow:
- 如何报告mysqli中的错误
- 如何使用PDO连接到MySQL (目的是报告正确的错误).
- How to report errors in mysqli
- How to connect to MySQL using PDO (with the aim of the proper error reporting).
简而言之，对于mysqi，必须在mysqli_connect()调用之前添加以下行:
In short, for mysqi the following line have to be added before mysqli_connect() call:
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
例如，对于PDO，必须设置正确的错误模式
while for PDO the proper error mode have to be set, for example
$pdo->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
从旧版mysql ext开始，
As of the old mysql ext,
要从mysql_query()中获取错误，必须使用mysql_error()函数.
因此，请始终以这种方式运行所有查询，至少直到开发出更高级的查询处理程序为止:
To get an error from mysql_query() you have to use mysql_error() function.
So always run all your queries this way, at least until you develop a more advanced query handler:
$query = "SELECT * FROM 'users'";
$result = mysql_query($query) or trigger_error(mysql_error()." ".$query);
您当前查询的问题是'users'部分.必须使用单引号来分隔字符串，而对于标识符，则必须使用反引号:
the problem with your current query is 'users' part. Single quotes have to be used to delimit strings while for the identifiers you have to use backticks:
SELECT * FROM `users`
为了在开发过程中看到这些错误，请在代码顶部添加以下行，以确保您可以看到发生的每个错误
In order to see these errors during development, add these lines at the top of your code to be sure you can see every error occurred
ini_set('display_errors',1);
error_reporting(E_ALL);
在生产服务器上，但是，第一行的值应从1更改为0
on the production server, however, the value on the first line should be changed from 1 to 0
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