mysql - 如何在更新查询中使用临时变量？

如何在执行Update语句时设置变量？
我好像搞不懂语法。我使用这个@tp变量来保存计算结果，它将在when条件下使用。
我想要这样的东西：

UPDATE users IU
INNER JOIN activity_stats DAS
    ON (IU.user_id=DAS.for_user_id), set
    @tp:= IU.total_subscription_time - (unix_timestamp()- IU.start_date),
    IU.time_period_left = CASE WHEN @tp > 0 THEN @tp ELSE 0 END,
    IU.used_time = (unix_timestamp() - IU.start_date),
    IU.status = CASE WHEN @tp > 0 THEN 'A' ELSE 'I' END,
    DAS.total_time_used = DAS.total_time_used + IU.used_time
WHERE IU.time_period_left > 0
  AND IU.status='A'

但是它说语法是错误的：

最佳答案

你能试试这个吗？

  UPDATE users IU
INNER JOIN activity_stats DAS
    ON (IU.user_id=DAS.for_user_id),
    IU.time_period_left = CASE WHEN (IU.total_subscription_time - (unix_timestamp()- IU.start_date)) > 0 THEN
                        (IU.total_subscription_time - (unix_timestamp()- IU.start_date))  ELSE 0 END,
    IU.used_time = (unix_timestamp() - IU.start_date),
    IU.status = CASE WHEN (IU.total_subscription_time - (unix_timestamp()- IU.start_date)) > 0 THEN 'A' ELSE 'I' END,
    DAS.total_time_used = DAS.total_time_used + IU.used_time
WHERE IU.time_period_left > 0
  AND IU.status='A'