$strSQL = "SELECT aaa,datetime FROM customer1";
$strSQL += " union SELECT bbb,datetime FROM customer2";
$strSQL += " union SELECT ccc,datetime FROM customer3";
$strSQL += " oder by 2";
$strSQL = "SELECT aaa,datetime FROM customer1";
$strSQL += " union SELECT bbb,datetime FROM customer2";
$strSQL += " union SELECT ccc,datetime FROM customer3";
$strSQL += " oder by 2";