Delicious Bookmark this on Delicious Share on Facebook SlashdotSlashdot It! Digg! Digg



PHP : Function Reference : MySQL Functions : mysql_close

mysql_close

Close MySQL connection (PHP 4, PHP 5, PECL mysql:1.0)
bool mysql_close ( [resource link_identifier] )

Example 1414. 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

Related Examples ( Source code ) » mysql_close












Code Examples / Notes » mysql_close

jonbarnett

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.


4dacres

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.

rons

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.


beer_nomaed _at_ hotmail _dot_ com

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.


levi

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"


bbodelcampo

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....


Change Language


Follow Navioo On Twitter
mysql_affected_rows
mysql_change_user
mysql_client_encoding
mysql_close
mysql_connect
mysql_create_db
mysql_data_seek
mysql_db_name
mysql_db_query
mysql_drop_db
mysql_errno
mysql_error
mysql_escape_string
mysql_fetch_array
mysql_fetch_assoc
mysql_fetch_field
mysql_fetch_lengths
mysql_fetch_object
mysql_fetch_row
mysql_field_flags
mysql_field_len
mysql_field_name
mysql_field_seek
mysql_field_table
mysql_field_type
mysql_free_result
mysql_get_client_info
mysql_get_host_info
mysql_get_proto_info
mysql_get_server_info
mysql_info
mysql_insert_id
mysql_list_dbs
mysql_list_fields
mysql_list_processes
mysql_list_tables
mysql_num_fields
mysql_num_rows
mysql_pconnect
mysql_ping
mysql_query
mysql_real_escape_string
mysql_result
mysql_select_db
mysql_set_charset
mysql_stat
mysql_tablename
mysql_thread_id
mysql_unbuffered_query
eXTReMe Tracker