使用 CROSS APPLY 的慢查询

Question

我有以下 SQL 代码，需要几秒钟才能执行：

SELECT instance.startdate
      ,instance.enddate 
FROM (select mr.id 
      FROM meeting_recurrence AS mr 
      inner JOIN meeting_details md ON md.id = mr.meeting_template_id 
      WHERE host_user_id=17) AS p 
CROSS APPLY GetRecurrenceMeetingInstances(p.id,'2018-11-09 11:00:00','2018-11-09 15:00:00') AS instance  
WHERE 21015 IS NOT NULL 
AND instance.meetingid <> 21015

上面例子中的内部select(select mr.id FROM meeting_recurrence...)returns即刻，有两个id。

运行 GetRecurrenceMeetingInstances() 分别使用这两个 id，returns 立即为空结果。

为什么运行整个语句比单独运行花费的时间长？

执行计划图片：https://imgur.com/a/3Ydym

Answer 1

似乎 CROSS APPLY 调用 GetRecurrenceMeetingInstances() 的次数比我想象的要多得多。我通过首先将内部 select 保存在局部变量中解决了这个问题：

DECLARE @innerresult table(meetingid int)
INSERT INTO @innerresult(meetingid) (select mr.id FROM meeting_recurrence AS mr inner JOIN meeting_details md ON md.id = mr.meeting_template_id 
    WHERE host_user_id=17)

INSERT INTO @timeslots (startdate,enddate) 
    SELECT instance.startdate,instance.enddate 
    FROM (select meetingid FROM @innerresult) AS p 
    CROSS APPLY GetRecurrenceMeetingInstances(p.meetingid,'2018-11-09 11:00:00','2018-11-09 15:00:00') AS instance

使用 CROSS APPLY 的慢查询

Slow query with CROSS APPLY

sql

cross-apply