Last updated: Fri, 20 Nov 2009

mysql_close

(PHP 4, PHP 5)

mysql_close — Close MySQL connection

Description

bool mysql_close ([ resource $link_identifier ] )

mysql_close() closes the non-persistent connection to the MySQL server that's associated with the specified link identifier. If link_identifier isn't specified, the last opened link is used.

Using mysql_close() isn't usually necessary, as non-persistent open links are automatically closed at the end of the script's execution. See also freeing resources.

Parameters

link_identifier: The MySQL connection. If the link identifier is not specified, the last link opened by mysql_connect() is assumed. If no such link is found, it will try to create one as if mysql_connect() was called with no arguments. If no connection is found or established, an E_WARNING level error is generated.

Return Values

Returns TRUE on success or FALSE on failure.

Examples

Example #1 mysql_close() example


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

The above example will output:

Connected successfully

Notes

Note: mysql_close() will not close persistent links created by mysql_pconnect().


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....

levi at alliancesoftware dot com dot au
29-Apr-2005 05:03


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:





<?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"

beer_nomaed _AT_ hotmail _DOT_ com
03-Dec-2004 07:26


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.

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