The connection id returned by this functions is needed by other ODBC functions. You can have multiple connections open at once as long as they either use different db or different credentials.
resource odbc_connect ( string $dsn , string $user , string $password [, int $cursor_type ] )
<?php
// Microsoft SQL Server using the SQL Native Client 10.0 ODBC Driver - allows connection to SQL 7, 2000, 2005 and 2008
$connection = odbc_connect("Driver={SQL Server Native Client 10.0};Server=$server;Database=$database;", $user, $password);
// Microsoft Access
$connection = odbc_connect("Driver={Microsoft Access Driver (*.mdb)};Dbq=$mdbFilename", $user, $password);
// Microsoft Excel
$excelFile = realpath('C:/ExcelData.xls');
$excelDir = dirname($excelFile);
$connection = odbc_connect("Driver={Microsoft Excel Driver (*.xls)};DriverId=790;Dbq=$excelFile;DefaultDir=$excelDir" , '', '');
?>