从数据库查找最小日期

Question

我有如下查询：

SELECT
    IsTestBatch,
    BatchID,
    CampaignID,
    IF(ActualTriggerDateTime IS NOT NULL,
       MIN(ActualTriggerDateTime),
       MIN(TriggerDateTime)) AS NextQueuedOn
FROM
    campaignbatches
WHERE
    Status IN (2,3)
GROUP BY
    CampaignID
ORDER BY
    IF(ActualTriggerDateTime IS NOT NULL, ActualTriggerDateTime, TriggerDateTime) ASC

if条件无法正常运行，并且MIN日期不符合我的预期。

我期望上面的记录，但是它从表中返回上一张图像的第一条记录：

Answer 1

由于聚合函数MIN()忽略了NULL的值，因此您可以尝试从 ActualTriggerDateTime 列中选择最小日期，在特殊情况下，所有值均为NULL在此列上，然后从 TriggerDateTime 列中选择最小值。

SELECT
    IsTestBatch,
    BatchID,
    CampaignID,
    IFNULL(MIN(ActualTriggerDateTime), MIN(TriggerDateTime)) AS NextQueuedOn
FROM
    campaignbatches
WHERE
    Status IN (2,3)
GROUP BY
    IsTestBatch, BatchID, CampaignID
ORDER BY
    NextQueuedOn ASC

Answer 2

所有选择列都将按子句分组

SELECT IsTestBatch,BatchID,CampaignID,
 coalesce(MIN(ActualTriggerDateTime),MIN(TriggerDateTime)) AS NextQueuedOn 
 FROM campaignbatches
WHERE Status IN (2,3)
   and IsTestBatch=1 and BatchID=42 -- as you want single row
 GROUP BY IsTestBatch,BatchID,
   CampaignID 
ORDER BY NextQueuedOn ASC