Running dbDelta on a different database then WordPress

query.php

<?php

	/*
	 * Using a different database with dbDelta
	 */
	 
	global $wpdb;
		
	require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
	
	$previous_wpdb = $wpdb;
	$wpdb = new wpdb('username','password','database','localhost');
		 		 
	$charset_collate = '';
	 		
	if ( ! empty( $wpdb->charset ) ) {
		$charset_collate = "DEFAULT CHARACTER SET {$wpdb->charset}";
	}
	
	if ( ! empty( $wpdb->collate ) ) {
		$charset_collate .= " COLLATE {$wpdb->collate}";
	}
		
	$sql = "CREATE TABLE test_table (
	  ID mediumint(9) NOT NULL AUTO_INCREMENT,
	  PRIMARY KEY ID (id)
	) ".$charset_collate.";";
	
	dbDelta( $sql );
	
	$wpdb = $previous_wpdb;

Good idea - helped me. Thanks.