警告:mysql_query():3 不是有效的 MySQL-Link 资源 [英] Warning: mysql_query(): 3 is not a valid MySQL-Link resource
问题描述
我遇到了这个奇怪的错误，我不知道它来自哪里:
I got this odd error and I can't figure out where it came from:
Warning: mysql_query(): 3 is not a valid MySQL-Link resource in (...)
3 怎么了?我不明白.有没有人自己遇到过这个错误?
What's up with the 3? I don't get it. Has anyone experienced this error themselves?
推荐答案
PHP 使用资源作为特殊变量来保存指向外部对象的链接，例如文件和数据库连接.每个资源都有一个整数 id.(文档)
PHP uses resources as a special variable to hold links to external objects, such as files and database connections. Each resource is given an integer id. (Documentation)
如果数据库连接失败，您可能会得到指定的变量不是有效的 MySQL-Link 资源"；错误，正如 Dan Breen 提到的，因为应该保存资源的变量为空.
If the database connection fails you'll likely get a "Specified variable is not a valid MySQL-Link resource" error, as Dan Breen mentioned, since the variable that is supposed to hold the resource is null.
$link = mysql_connect('localsoth','baduser','badpass'); // failed connection
$result = mysql_query("SELECT 1", $link); // throws error
由于您在错误消息中获得了特定的资源 ID，因此数据库连接可能出于某种原因意外关闭.您的程序仍然有一个带有资源 ID 的变量，但外部对象不再存在.这可能是由于 mysql_close() 在调用 mysql_query 之前的某处调用，或者关闭连接的外部数据库错误.>
Since you're getting a specific resource ID in the error message, the database connection likely closed unexpectedly for some reason. Your program still has a variable with a resource ID, but the external object no longer exists. This may be due to a mysql_close() call somewhere before the call to mysql_query, or an external database error that closed the connection.
$link = mysql_connect();
mysql_close($link);
// $link may still contain a resource identifier, but the external object is gone
mysql_query("SELECT 1", $link);
重用连接
mysql 扩展和 mysql_connect() 的一个问题是，默认情况下，如果您在连续调用中传递相同的参数，它将重新使用现有连接而不是创建一个新连接(文档).这可以通过将 true 传递给 $new_link 参数来解决.
我自己在一个测试系统上遇到过这个问题，其中来自生产中两个独立数据库的数据被合并到一个测试服务器上，并且在测试中，mysql_xxx() 函数调用相互交叉并破坏了系统.
Reusing Connections
An issue with the mysql extension and mysql_connect() is that by default if you pass the same parameters in successive calls, it will re-use the existing connection rather than create a new one (Documentation). This can be fixed by passing true to the $new_link parameter.
I encountered this myself on a test system where the data from two separate databases in production were combined on to one test server, and in testing the mysql_xxx() function calls walked over each other and broke the system.
$link1 = mysql_connect('localhost','user','pass'); // resource id 1 is given
$link2 = mysql_connect('localhost','user','pass'); // resource id 1 is given again
mysql_close($link2); // the connection at resource id 1 is closed
mysql_query("SELECT 1", $link1); // will fail, since the connection was closed
使用$new_link:
$link1 = mysql_connect('localhost','user','pass'); // resource id 1 is given
$link2 = mysql_connect('localhost','user','pass', true); // resource id 2 is given
mysql_close($link2); // the connection at resource id 2 is closed
mysql_query("SELECT 1", $link1); // the connection at resource id 1 is still open
顺便说一句，我建议使用 MySQLi 扩展或 PDO 如果可能的话.MySQL 扩展已经很老了，无法利用 MySQL 4.1.3 版之后的任何功能.看http://www.php.net/manual/en/mysqli.overview.php 了解有关三个接口之间差异的一些详细信息.
As an aside, I would recommend using the MySQLi extension or PDO instead, if possible. The MySQL extension is getting pretty old, and can't take advantage of any features past MySQL version 4.1.3. Look at http://www.php.net/manual/en/mysqli.overview.php for some details on the differences between the three interfaces.
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