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MySQL in and limit performance

Posted on 2009-07-09
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Last Modified: 2012-05-07
HI: A performance questions: In MySQL, when display a list, I have two stratergy to display it:
SQL One:
select * from tablename where id in (some arrays);  

SQL Two:

select * from tablename limit 10,10;

Questions: Which query is faster?

In query one: If array size is 20 and 100, does it mean 100 is 5 times slower than 20.
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Question by:JianJunShen
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7 Comments
 
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theGhost_k8 earned 400 total points
ID: 24813073
Use explain to check query performances.
"in" should use indexes to perform quicker.
"limit n,m" will require full table scan which we try to avoid normally.

The difference wont be that large.
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by:theGhost_k8
theGhost_k8 earned 400 total points
ID: 24813106
Mean while about pagination have a look at this:
http://www.percona.com/ppc2009/PPC2009_mysql_pagination.pdf
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Assisted Solution

by:snoyes_jw
snoyes_jw earned 100 total points
ID: 24813165
The second one is probably faster as written, but usually if you have LIMIT you also have ORDER BY, and then it's probably slower. Depends on if there are indexes involved and how big the table is.

It's hard to say exactly how different looking up 20 values vs. 100 values would be; the easiest thing would be to just try it and see.
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Author Comment

by:JianJunShen
ID: 24814346
Hi theGhost_k8:

What about I have less than 10,000 records. Does that worthe indexing in order for faster speed? Or in other way, if my table rows are less than 10,000, use in or use limit?
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by:theGhost_k8
theGhost_k8 earned 400 total points
ID: 24820439
Have you checked actually executing queries?
I see limit n,m easily manageable - considering there'd be less performance differences.
In case of "order by", you check the difference in both the queries.
Make sure, you keep the query_cache off / use SQL_NO_CACHE for comparison.
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Author Comment

by:JianJunShen
ID: 24843688
Hi:  experts:

Do you have some links to tell how to check the SQL performance? How faster it is and how many memory it consumes?
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by:theGhost_k8
theGhost_k8 earned 400 total points
ID: 24846171
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