mysql affected rows_mysql UPDATE后通过mysql_affected_rows判断是否成功，没有则INSERT ，结果出问题了...

mysql UPDATE后通过mysql_affected_rows判断是否成功，没有则INSERT ，结果出问题了，表行数成倍的增长，代码如下，求解

//数据写入数据库

function save_db($currencyname_en,$currencyname_cn,$buyingrate,$sellingrate,$middlerate)

{

//更新

$query_update = ' UPDATE '. TABLENAME .' SET '

.' buyingrate=' .$buyingrate .','

.' sellingrate=' .$sellingrate .','

.' middlerate=' .$middlerate .','

.' lastupdatetime="' .date('Y-m-d H:i:s',time()) .'"'

.' WHERE currencyname_en="' .$currencyname_en .'"';

mysql_query($query_update);

if(mysql_affected_rows()!=1)//更新不成功，尝试插入

{

$query_insert = 'INSERT INTO ' . TABLENAME . '(currencyname_en, currencyname_cn, buyingrate, sellingrate, middlerate, lastupdatetime) VALUES (

"'.$currencyname_en.'",

"'.$currencyname_cn.'",

"'.$buyingrate.'",

"'.$sellingrate.'",

"'.$middlerate.'",

"'.date('Y-m-d H:i:s',time()).'"

)';

mysql_query($query_insert);

}

if(mysql_affected_rows()!=1)

{

$err .= "
插入或者更新".$currencyname_en."-".$key."currencyname_cn";

}

}