Put several query result in one JSON file using PHP

I am using a PHP file to generate JSON files.  Now I have three queries.  I generate one JSON file for each of the queries.

I'm just wondering if it is possible to generate one JSON file for all three queries.

Following is the code I use to generate JSON files.  Thanks.

        $arr = array();
	$rs = mysql_query("
		SELECT
			Column
		FROM
			Table;
	");
	while($obj = mysql_fetch_object($rs)) {
		$arr[] = $obj;
	}

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