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    mysql_close

    (PHP 4, PHP 5)

    mysql_close — 关闭 MySQL 连接

    警告

    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 指南来获取更多信息。用以替代本函数的有：

    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。

    建立非持久性的 MySQL 连接，会在 PHP 执行完毕后自动销毁，所以手动关闭连接，并释放资源是可选的。但是还是推荐你在代码中显性的执行该操作，这对提高代码性能有帮助。参考文档 资源释放

    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。

    示例

    示例 #1 mysql_close() 示例

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

    以上示例会输出：

    Connected successfully

    注释

    注意:

    mysql_close() 不会关闭由 mysql_pconnect() 建立的持久连接。 有关其他详细信息，请参阅有关持久连接的手册页。

    参见

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    User Contributed Notes 6 notes

    up
    9
    bbodelcampo at yahoo dot co dot uk
    19 years ago
    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....
    up
    -4
    Anonymous
    14 years ago
    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.
    up
    -5
    mdes[SPAM]saintes at gmail dot com
    14 years ago
    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.
    up
    -5
    beer_nomaed _AT_ hotmail _DOT_ com
    20 years ago
    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.
    up
    -7
    omega99999 at gmail dot com
    13 years ago
    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)
    up
    -8
    levi at alliancesoftware dot com dot au
    19 years ago
    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"
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