Loading multiple SQL databases for a query

Question

The background here is that we use a SQL to run a diary and the following commands bring up the results from one specific SQL

if ($_SERVER['HTTP_HOST'] == "localhost") {
    $GLOBALS['dbUsername']     = "admin";
    $GLOBALS['dbPassword']     = "admin";
    $GLOBALS['dbHost']         = "localhost";
    $GLOBALS['dbDatabase']     = "Tracker";
}
else {
    $GLOBALS['dbUsername']     = "admin";
    $GLOBALS['dbPassword']     = "admin";
    $GLOBALS['dbHost']         = "localhost";
    $GLOBALS['dbDatabase']     = "store_3";
}

However we have around 26 of these using "store_1" - "store_26" So to look through them all can take a while. I wanted to simply load multiple at the same time but my SQL + PHP knowledge is not that great

I thought that:

$GLOBALS['dbDatabase']     = "store_3";"store_4"

Would allow me to review more than 1 but this fails. The only other reference to dbDatabase is slightly later in the code

$conn = mysql_connect($GLOBALS['dbHost'], $GLOBALS['dbUsername'], $GLOBALS['dbPassword']);
$data = mysql_select_db($GLOBALS['dbDatabase']);

So I am presuming if I log into multiple databases at the beginning I would also need a way to include them in this statement, any help would be much appreciated.

Answer 1

You can access tables of other database using dbname.tablename

But the databases you want to access should be on same server.

For example:

// Establish connection
$conn = mysql_connect($GLOBALS['dbHost'], $GLOBALS['dbUsername'], $GLOBALS['dbPassword']);

// Select Any one database. Let's say `store_1`
$data = mysql_select_db($GLOBALS['dbDatabase']);

$sql1 = "SELECT * FROM store_1.tablename";
$sql2 = "SELECT * FROM store_2.tablename";
$sql3 = "SELECT * FROM store_4.tablename a JOIN store_5.tablename b ON a.id = b.id";