Re: [PHP-DB] Multiple instances of mysql_connect() in single PHP document.

2009/11/11 Chris <[email protected]>:
> Andy Shellam (Mailing Lists) wrote:
>>
>> Hi,
>>
>>>
>>> If the databases are in the same mysql server, then you could qualify
>>> the table select with the database name and simply re-use the
>>> connection
>>>
>>> select db_name.table_name.field from db_name.table_name [where]
>>
>> No offence, but if I saw this in an application's source code, I'd run a
>> mile.
>
> Plus the assumption that they are on the same server and that the user
> you're connecting with has access to both databases..
>
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>

If it comes to that, if you are writing SQL code in PHP rather than
abstracting it or using stored procedures/views/etc. ...

Essentially the issue is 2 identical connections are not actually 2
identical connections.

They are 2 references to a single connection.

So, changing the DB via 1 resource changes the db for both resources.

NOTE: IDENTICAL. If the server or username is different, then that
results in a separate connection.

<?php
$conn1 = mysql_connect($server, $username, $password);
$conn2 = mysql_connect($server, $username, $password); // Is the same
connection as $conn1
mysql_select_db($db1, $conn1); // Both connection resources are now
looking at db1.
mysql_select_db($db2, $conn2); // Both connection resources are now
looing at db2.

_ONE_ solution is to use fully qualified names (you can use constants
if you don't like hard-coding the db name in the query).

Another option is to set the new_link flag on the mysql_connect() call.

That way you will have 2 separate connections.

<?php
$conn1 = mysql_connect($server, $username, $password, true);
$conn2 = mysql_connect($server, $username, $password, true); // Is NOT
the same connection as $conn1
mysql_select_db($db1, $conn1); // Points to db1 for connection1
mysql_select_db($db2, $conn2); // Points to db2 for connection2




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