php - 将所有值加在一起 ​​SQL SELECT

Question

如何将所有金额加在一起，以便此选择脚本返回所有单独的提款金额而不是返回其中所有金额加在一起的一个数字？

<?php
$end_date = strtotime($nextdate);
$start_date = strtotime($statement_date);
$username = $usr['username'];
$result = mysql_query("SELECT * FROM `usr_withdraw` WHERE `timestamp` > '$start_date' AND `timestamp` < '$end_date' AND `username` = '$username'")or die(mysql_error());

while($balance = mysql_fetch_array( $result )) { 
    echo $balance['amount'];
}
?>

Answer 1

要仅返回 1 行以及所有金额的总和，请使用 SQL sum()功能。

SELECT sum(amount) FROM `usr_withdraw` WHERE ...