如何在 SELECT 中声明变量？

Question

我有一个计算报告刷新时间的长查询，如果报告没有在“计划”时间刷新，那么它会延迟显示，根据以下情况：

SELECT
RefreshStartStatus      =   CASE 
                                WHEN CS.StartTime > CURRENT_TIMESTAMP THEN 'STARTING LATER'
                                WHEN DATEDIFF(MINUTE, CS.StartTime, SA.TodayFirstRunTime) < 30 THEN 'Less than half hour late!' -- less than 30 mins late
                                WHEN DATEDIFF(MINUTE, CS.StartTime, SA.TodayFirstRunTime) >= 30 THEN 'More than half hour Late!' -- 30 mins late
                                ELSE '???'
                                END
FROM #CSTempTable CS

LEFT OUTER JOIN #SubscriptionAggTempTable SA
    ON SA.SubscriptionID = CS.SubscriptionID

我想进一步增强这一点，并显示实际时间有多晚。

由于我使用过脚本（例如 PowerShell），所以它会很简单

WHEN DATEDIFF(MINUTE, CS.StartTime, SA.TodayFirstRunTime) < 30 THEN "$(DATEDIFF(MINUTE, CS.StartTime, SA.TodayFirstRunTime)) late!"

但当然，这里的 SQL 查询不是这种情况，那么我将如何输出延迟多长时间的实际值？我想过像这样声明和设置一个标量变量：

DECLARE @timing int;
SET @timing = DATEDIFF(MINUTE, CS.StartTime, SA.TodayFirstRunTime);

WHEN @timing < 30 THEN @timing + ' mins late!'

但我不知道如何在 SELECT 语句中执行此操作，因为由于执行差异所需的连接，该值是在其中生成的...

结果是这样的：

SELECT

DECLARE @timing int;
SET @timing = DATEDIFF(MINUTE, CS.StartTime, SA.TodayFirstRunTime);

RefreshStartStatus      =   CASE 
                                WHEN CS.StartTime > CURRENT_TIMESTAMP THEN 'STARTING LATER'
                                WHEN timing < 30 THEN @timing + ' mins late! a little late' -- less than 30 mins late
                                WHEN timing >= 30 THEN timing + ' mins Late! VERY LATE!' -- 30+ mins late
                                ELSE '???'
                                END
FROM #CSTempTable CS

LEFT OUTER JOIN #SubscriptionAggTempTable SA
    ON SA.SubscriptionID = CS.SubscriptionID

Answer 1

如果我没听错的话，你可以使用VALUES() 和横向连接只进行一次计算：

SELECT
    CASE 
        WHEN CS.StartTime > CURRENT_TIMESTAMP THEN 'STARTING LATER'
        WHEN x.timing <  30 THEN 'Less than half hour late!' 
        WHEN x.timing >= 30 THEN 'More than half hour Late!'
        ELSE '???'
    END as RefreshStartStatus,
    CASE WHEN CS.StartTime <= CURRENT_TIMESTAMP THEN CONCAT(x.timing ' mins late') END as info
FROM #CSTempTable CS
LEFT OUTER JOIN #SubscriptionAggTempTable SA ON SA.SubscriptionID = CS.SubscriptionID
CROSS APPLY (VALUES (DATEDIFF(MINUTE, CS.StartTime, SA.TodayFirstRunTime))) as x(timing)