在 where 原因中使用交叉应用列时查询很慢

Question

This is my query. Every row in tblSMSSendQueueMain may have some record in tblSMSSendQueueMainSendStatus. QueueID in tblSMSSendQueueMainSendStatus is foreign key for ID in tblSMSSendQueueMain

select top 10 ID from tblSMSSendQueueMain q
CROSS Apply
(
    select top 1 SendStatus from tblSMSSendQueueMainSendStatus where QueueID = q.ID order by ID desc
) qs
where qs.SendStatus = 1 order by ID Desc

This query take a long time to run. But if I write qs.SendStatus = 5 its fast.

I have nonclustered index on tblSMSSendQueueMainSendStatus as below

CREATE NONCLUSTERED INDEX [IX_tblSMSSendQueueMainSendStatus_SendStatus] ON [dbo].[tblSMSSendQueueMainSendStatus]
(
    [QueueID] ASC,
    [ID] DESC
)
INCLUDE([SendStatus]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]

Whats wrong? Or is there is a better way to write this query, joining multi tables values and filter the result.

Thanks

Answer 1

As I don't have your execution plans. I am just providing an alternative way of INNER JOIN. Test your query for performance.

;WITH CTE_QueueStatus AS
(
select q.ID, qs.SendStatus, ROW_NUMBER() OVER(PARTITION BY qs.QueueID ORDER BY qs.ID desc)  as rnk from tblSMSSendQueueMain q
INNER JOIN tblSMSSendQueueMainSendStatus qs ON  qs.QueueID = q.ID
)
SELECT top 10 ID 
FROM CTE_QueueStatus AS c
where qs.SendStatus = 1 -- only sendstatus =1 is selected
and c.rnk = 1 -- Only the top status is selected
order by ID Desc