php - 无法将 1 增量添加到 SQL 中的用户变量

Question

这可能是由于变量@count未被识别为整数，但在我的研究中，我遇到了许多类似于@count = @count + 1的示例>;这就是为什么我很困惑为什么这会在引入时破坏我的代码:

$setCount = "SELECT @count:=5";
$uncategorise = "UPDATE pictures
    SET category = '0',
    pictureorder = @count,
    @count:=@count+1
    WHERE category = '$categoryID'
    AND username = '$username';
$queryCount = mysql_query($setCount) or die(mysql_error());
$queryUncat = mysql_query($uncategorise) or die(mysql_error());

Answer 1

因为这是一个 user defined variable ,
仅适用于相同的 session /连接

You can store a value in a user-defined variable in one statement and then refer to it later in another statement. This enables you to pass values from one statement to another. User-defined variables are connection-specific. That is, a user variable defined by one client cannot be seen or used by other clients. All variables for a given client connection are automatically freed when that client exits.

有一个简单的解决方案 - php mysqli_multi_query