值仍然插入，即使查询包含在if语句中，这应该阻止它这样做 - Value still inserting, even though query encased in if statement which should stop it from doing so?

Value still inserting, even though query encased in if statement which should stop it from doing so?

我真的不知道这是怎么回事，我已经绞尽脑汁想了好长时间了;

我有变量$overflow = $_POST['overflow'];，然后是以下代码:

if($overflow != "" || $overflow != "Overflow link"){
    $query = "DELETE FROM links WHERE overflow='YES'";
    $result = mysql_query($query) or die(mysql_error());
    $query = "INSERT INTO links (link, overflow) VALUES ('$overflow','YES') ON DUPLICATE KEY UPDATE overflow=VALUES(overflow)";
    $result = mysql_query($query) or die(mysql_error());
}

这个想法是，如果$overflow是空的或持有默认值，它不被插入，但如果它是一个有效值，它已经存在的条目被删除(因为我不能使列唯一)，它被重新插入。

有人知道为什么它插入任何值吗?

任何帮助都将非常感激!

"If not empty or not some value".

不能同时为空和 "some value"，所以这个条件总是为真。你要找的是:

if ($overflow != "" && $overflow != "Overflow link")

if(!empty($overflow) && $overflow != "Overflow link"){
    $query = "DELETE FROM links WHERE overflow='YES'";
    $result = mysql_query($query) or die(mysql_error());
    $query = "INSERT INTO links (link, overflow) VALUES ('$overflow','YES') ON DUPLICATE KEY UPDATE overflow=VALUES(overflow)";
    $result = mysql_query($query) or die(mysql_error());
}