Question

I seem to go back and forth on this, sometimes it works for me, often it doesn’t and I can’t figure out how/why I can get it to work sometimes, and at other times it won’t.

I have 5 databases, and need to grab data from each of them during a maintenance routine.
For each of the databases, I have an external file which contains all the db connection code which I include in my page.

The includes look like this

$SGcon = mysql_connect("localhost","root","");

if (!$SGcon)
  {
  die('Could not connect: ' . mysql_error());
  }

mysql_select_db("sGopen", $SGcon);

For each database I provide a different varaible, so the next database will be

$PTcon = mysql_connect("localhost","root","");

if (!$PTcon)
  {
  die('Could not connect: ' . mysql_error());
  }

mysql_select_db("pTsecond", $PTcon);

Then when i call my query, I use

 
mysql_query($getQuery,  $PTcon);
mysql_query($secondQuery, $SGcon);

The problem I’m running into is that I’m not getting the correct database used for the query , it seems my script is using the databases which was added to the page last.

Is there a better way for me to switch the database connection to be used?

There is lots of back and forth between the databases as I’m comparing data from one db to data in another, so i’m trying to be efficient with this as well.

Thanks
Pete

Answer 1

By default, if you pass the same arguments to mysql_connect as a previous call it’ll return a cached connection if available, rather than creating a new one. So both queries are running against whichever database you last passed to mysql_select_db.

Passing new_link=true will avoid this behaviour, although database connections can be expensive so you should try to keep as few open as reasonably possible.

The detailed explanation for new_link:

If a second call is made to
mysql_connect() with the same
arguments, no new link will be
established, but instead, the link
identifier of the already opened link
will be returned. The new_link
parameter modifies this behavior and
makes mysql_connect() always open a
new link, even if mysql_connect() was
called before with the same
parameters. In SQL safe mode, this
parameter is ignored.