mysql_close()

(PHP 4, PHP 5)

关闭 MySQL 连接

Warning
本扩展自 PHP 5.5.0起已废弃，并在自 PHP 7.0.0 开始被移除。应使用MySQLi或PDO_MySQL扩展来替换之。参见MySQL：选择 API指南以及相关 FAQ来获取更多信息。用以替代本函数的有：
mysqli_close()
PDO:为 PDO 对象设置一个NULL值

说明

mysql_close([resource $link_identifier= NULL]): bool

mysql_close()关闭指定的连接标识所关联的到 MySQL 服务器的非持久连接。如果没有指定$link_identifier，则关闭上一个打开的连接。

通常不需要使用mysql_close()，因为已打开的非持久连接会在脚本执行完毕后自动关闭。参见释放资源。

参数

$link_identifier: MySQL 连接.如果该连接标识符未给出,将使用最近一次mysql_connect()建立的连接.如果没有找到可使用的连接,将产生一个E_WARNING错误.

返回值

成功时返回TRUE，或者在失败时返回FALSE。

范例

Example #1 mysql_close()例子

<?php
$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
if (!$link) {
    die('Could not connect: ' . mysql_error());
}
echo 'Connected successfully';
mysql_close($link);
?>

以上例程会输出：

Connected successfully

注释

Note:
mysql_close()不会关闭由mysql_pconnect()建立的持久连接。

参见

mysql_connect()打开一个到 MySQL 服务器的连接
mysql_free_result()释放结果内存

A little note about multiple simultaneous connections to different hosts...
I work on a site that pulls content primarily from one db but uses a db on a foreign server to verify licensing. One might expect the following to work:
<?php
// Open the connection to the primary db
$res1 = mysql_connect($host1, $user1, $pass1);
mysql_select_db($db1);
// Open connection to the license server
$res2 = mysql_connect($host2, $user2, $pass2);
mysql_select_db($db2, $res2);
// Pull license data and close when done
mysql_query($check_sql, $res2);
// ...
mysql_close($res2);
// Now pull content from the primary db
// Not specifying the resource should default to the last open db
mysql_query($query); 
// ...
?>
Turns out this last query, since it cant find an active connection, will try to connect with mysql_connect() with no paramaters. But if instead you do it as mysql_query($query, $res1), or alternatively, run the mysql_connect for this host again then it works fine. Thus, it doesnt seem to be possible to have code with an overarching "global" db connection interspersed with temporary connections to another host/db....

At least with PHP5.3.2 and Windows connecting by tcp, you should always use this mysql_close() function to close and free up the tcp socket being used by PHP. Garbage collection after script execution does not close the tcp socket on its own. The socket would otherwise remain in 'wait' state for approximately 30 seconds, and any additional page loads/connection attempts would only add to the total number of open tcp connections. This wait time does not appear to be configurable via PHP settings.

Be careful when using multiple links to connect to same database (with same username). Unless you specify explicitly in mysql_connect() to create a new link, it will return an already open link. If that would be closed by mysql_close(), it will also (obviously) close the other connection, since the link is the same.
Had lot of trouble figuring it out, since in <=4.3.6 there was a bug which didn't close the connection, but after the patch to >=4.3.7, all my application broke down because of a single script that did this.

i just came over a problem that i had with apache.
It crashs and said :
"Parent: child process exited with status 3221225477 -- Restarting."
the error came from the extesion php_mysql.dll
i didn't understand what was the reason of that crash..
Then, i debug the script that i had downloaded and i noticed that that was the function mysql_close() which caused the problem.
The solution is, to send to it the link identifier which is optionnal in the description but cause a crash with no commentary.
Thanks to agneady.

The variable is definitely not optional in 5.3... Caused me a bit of a headache when I was debugging until I realized it was the close function that was causing a hang. So if using just:
<?php
mysql_connect(<...>);
mysql_close();
?>
Use:
<?php
$connection = mysql_connect(<...>);
mysql_close($connection);
?>
(where $connection is any variable of your choice)

As at 5.0.x and 4.3.x: This function should never be used with shared links; instead you should set your link variables to null.
(This explains red's and beer's () problems in previous comments)
 Here is how shared links work:
 - Each link is a resource. mysql_connect() by default looks for a resource with the same paramaters. If one exists, it will return the existing resource. 
 - Every assignment of that resource to a variable increases the resource's reference count.
 - When the reference is decremented to zero, the underlying TCP/socket connection is closed.
  - Every assignment of a variable away from that resource decrements the reference count. (This includes a function level variable going out of scope)
  - mysql_close() also decrements the reference count.
Note the last two points: mysql_close() _and_ reassignment of a variable decrement the link's reference count.
A common mistake is a function like:
<?php
function dothings() {
 $link = mysql_open(...);
 // .. do some queries ..
 mysql_close($link)
 $link = null;
}
?>
this will decrement the counter twice, possibly closing the underlying connection and causing errors in other parts of the program.
http://bugs.php.net/bug.php?id=30525 "this is not a bug but just how it works"