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What's the difference between IN and INNER JOIN in my case?
In my MySQL database, table events has a composite index with columns closingeventid, timeStart and eventCode. There are more than 21 million rows in table events.
Here is two SQLs, if I run the first one in MySQL command line, the Mem Usage of process mysqld-nt.exe increases gradually with 10 M per second, it goes up around 1.6 G then plummets to around 30 M. Then the command line returns a Out of Memory exception.
But, it's ok if I use the second SQL, with INNER JOIN instead of IN. It seems IN clause doesn't hit any index.
Why? Any idea to monitor MySQL execution process like execution plan of MS SQL?
SELECT COUNT(*) AS 'cnt'
FROM events
WHERE
(timeStart < '2010-09-22 14:29:10’)
AND (closingeventid IS NULL)
AND (eventcode IN (SELECT DISTINCT evtcclosed FROM eventclose))`
VS
SELECT COUNT(1) AS 'cnt'
FROM events
inner join
(SELECT DISTINCT evtcclosed FROM eventclose) ec
ON ec.evtcclosed = events.eventcode
WHERE (timeStart < '2010-09-22 14:29:10’) AND (closingeventid IS NULL)
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What's the difference between IN and INNER JOIN in my case?