PHP&；MySQL：将表中的一行设置为由$u POST['；username'；]指定的变量

确保转义任何变量。否则php会将其解析为字符串：）

试试这个，以后再阅读手册，它非常有用：）

mysqli_fetch将被弃用。 这是手册

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首次获取值/记录时。修改它，然后重新输入。您必须注意并发/竞争条件。

<?php
//The victim's name, taken from a textfield
$victim = $_POST['username'];
//The ammount to be withdrawn from the user
$ammount = 2000;

if (isset($_POST['submit'])) {

mysql_query("UPDATE users SET money = money-$ammount WHERE username = '$victim'");
echo "You stole $ammount from $victim";
} else {
echo "Write the username of the person you're trying to steal money from..";
}

?>

$victimsMoney = mysql_query("SELECT money FROM users WHERE username = '$victim'");

$victimsMoney = mysql_query("SELECT money FROM users WHERE username = '".$victim."'");
while($fetch = mysqli_fetch_assoc($victimsMoney)){
                echo $fetch['money'];
}