On 1/26/2012 9:28 AM, Stephen Russell wrote:
<snipped>
>>> UPDATE MyTable SET MyFactor = 1.23456 WHERE Field1 = 'VALUE' AND Field2
>>> IN ("VALUE2","VALUE3")
>>>
>>> The EXPLAIN says it won't use the combined index. But for simpler
>>> UPDATEs where it's just one value for Field2 and using an =, it says it
>>> WILL use the index. For example, this SQL would utilize the compound
>>> index:
>>>
>>> UPDATE MyTable SET MyFactor = 1.23456 WHERE Field1 = 'VALUE' AND Field2
>>> = "VALUE2"
> ---------------------------------
>
> Would it be better to to run separate updates?
> UPDATE MyTable SET MyFactor = 1.23456 WHERE Field1 = 'VALUE'
> AND Field2 = "VALUE2" ,"VALUE3"
>
> UPDATE MyTable SET MyFactor = 1.23456 WHERE Field1 = 'VALUE'
> AND Field2 = "VALUE3"
>
> I read in your first url that the size of the param may be your biggest issue.
I thought the same thing, Steve. Perhaps better to run separate updates
for the 2 and 3 values for the FIELD2 multiple scenario. The math
person inside of me says "Better to pass the data once (reminds me of
"Big O notation" learned in college days), but indexes change that plan
I suppose.
--
Mike Babcock, MCP
MB Software Solutions, LLC
President, Chief Software Architect
http://mbsoftwaresolutions.com
http://fabmate.com
http://twitter.com/mbabcock16
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