Last updated: Fri, 18 Jul 2008

mysql_close

(PHP 4, PHP 5, PECL mysql:1.0)

mysql_close — MySQL 接続を閉じる

説明

bool mysql_close ([ resource $link_identifier ] )

mysql_close() は、指定した link_identifier が指す MySQL データベースへの非持続的リンクを閉じます。 link_identifier が指定されない場合、最後にオープンされたリンクが使用されます。

持続的でないリンクはスクリプトの実行終了時に自動的に閉じられるので、通常は mysql_close() を使用する必要はありません。リソースの解放を参照ください。

パラメータ

link_identifier: MySQL 接続。指定されない場合、mysql_connect() により直近にオープンされたリンクが指定されたと仮定されます。そのようなリンクがない場合、引数を指定せずに mysql_connect() がコールした時と同様にリンクを確立します。リンクが見付からない、または、確立できない場合、 E_WARNING レベルのエラーが生成されます。

返り値

成功した場合に TRUE を、失敗した場合に FALSE を返します。

例

例1 mysql_close() の例


<?php
$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
if (!$link) {
    die('接続できませんでした: ' . mysql_error());
}
echo '接続に成功しました';
mysql_close($link);
?>

上の例の出力は以下となります。

接続に成功しました

注意

注意: mysql_close() は、mysql_pconnect() により生成された持続的リンクを閉じません。

参考

mysql_connect

mysql_client_encoding

Last updated: Fri, 18 Jul 2008

add a note User Contributed Notes
mysql_close

jonbarnett at gmail dot com
17-Jan-2007 06:25


RonS is mostly incorrect about mysql_close.  It's not necessarily good programming practice to always explicitly close your database connect as it might be in other languages.  Your connection will be closed as soon as your script is finished, so there is almost never a need to call mysql_close at the end of a script.



If you have a script that does a lot of queries, it's dangerous to overuse the mysql_close function, as constantly opening and closing a connection can cause a lot of overhead, especially if you're connecting to a remote database.  If you are already connected to a database and try to use mysql_connect again on the same database, then the same connection will be returned, and no new connection will be opened.  So, it's safe to overuse mysql_connect without overusing mysql_close.



If you need to open multiple connections to the same database, then create two connections with mysql_connect with the extra boolean argument to force a new connection to be made without reusing the old connection.



The only compelling reason for using mysql_close is if your script is assuredly finished with the connection, but still has a lot of processing left to do.  It is almost never beneficial to open and close the same connection throughout a script.

RonS
21-Aug-2006 04:38


I just got caught with the "connection to the same database" issue. I need to do a lookup to a master database for syncing issues, but there was a possibility a conenction to the master could be open elsewhere.  When I closed "my connection" it closed the "other connection" as well.



My goodness, this violates every principle in modern programming technique.  All functions can't possibly be smart enough to know if there is an existing connection to a database, and who the user is and all other parameters.



It is, however, good programming practice to close your database connections after you're done with them, a practice that I'll have to avoid allowing the program's termination to close the db since I can't tell if the return from mysql_connect() has given me my own resource or a pre-existing one.  Absolutely preposterous.



Since this is the lowest-level access to the database in the language, it should do as requested.

bbodelcampo at yahoo dot co dot uk
13-Dec-2005 05:20


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:



// 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....

4dacres at gmail dot com
12-Oct-2005 02:23


Read http://bugs.php.net/bug.php?id=30525, and wow... It might be 'just how it works', but this reads like a broken implementation. cameron2 has it right, with this implementation cleaning up connections with mysql_close() can never be done, esp. if the connection is passed to a routine that you have no visibilty into.  You just never know if setting the variable to null or calling mysql_close() is going to error the script.

levi at alliancesoftware dot com dot au
29-Apr-2005 12:03


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:

<?

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"

beer_nomaed _AT_ hotmail _DOT_ com
03-Dec-2004 01:26


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.

add a note

mysql_connect

mysql_client_encoding

Last updated: Fri, 18 Jul 2008