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i am trying to teach myself SQL and of course I would like to follow best practices.

I have created two querys to find the latest record :

select * from AppSurvey where 
DateLastUsed >= ( SELECT MAX(DateLastUsed) FROM AppSurvey)

and 

select top 1 * from AppSurvey order by DateLastUsed desc

is one of these methods more efficent than the other or does it really matter

fishhead
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    These are actually two different queries, if DateLastUsed isn't unique. So, apples to oranges. The top one can select many surveys while the bottom one will only sample one. – Mark Canlas Jan 15 '10 at 00:16
  • The first query could return more than 1 record, so they actually don't do the same thing. In MS-SQL, the second query is more efficent – Sparky Jan 15 '10 at 00:17

2 Answers2

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The first one could get more than one row, if your DateLastUsed column isn't unique.

Matt Hamilton
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There is a similiar post on this site to what you are trying to get at.

For autoincrement fields: MAX(ID) vs TOP 1 ID ORDER BY ID DESC

The preferred answer seems to be: "In theory, they will use same plans and run almost same time"

Community
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Jeremy Samuel
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