Chris, a couple of thoughts -
First, your index on the section is doing you no good (at this time)
since
all the values are the same. You may already know that, but thought I'd
mention it.
Second, my theory on why query #1 is faster - if all your prices range
from
1 up, and you're querying for prices greater than 0, then MySQL can just
return the first 30 rows after sorting them.
The second query, where you are looking for prices greater than 1,
MySQL has
to sort and then examine a number of rows until it finds enough matching
rows (price > 1) to satisfy your query. This likely takes a little bit of
time. How many rows do you have with price = 1? It would have to
scan over
that many before it could start satisfying your query, if you think about
it.
HTH,
Dan
On 9/10/07, Chris Hemmings <[EMAIL PROTECTED]> wrote:
Hello,
I have a table, currently holding 128,978 rows... In this table, I
have a
section column (int) and a price column (int). Every row has a
section of
1
currently, every row has a price, ranging from 1 to 10,000.
I have an index on both columns separately.
Have a look at these two queries, can someone tell me why there is
such a
difference in speed of execution? (Note difference in price qualifier)
########################################
SELECT *
FROM `table1`
WHERE price >0
AND section =1
ORDER BY price
LIMIT 0 , 30
Showing rows 0 - 29 (128,978 total, Query took 0.9462 sec)
Explain output: 1 SIMPLE table1 ALL section,price NULL NULL NULL 96734
Using
where; Using filesort
########################################
SELECT *
FROM `table1`
WHERE price >1
AND section =1
ORDER BY price
LIMIT 0 , 30
Showing rows 0 - 29 (128,949 total, Query took 0.0008 sec)
Explain output: 1 SIMPLE table1 ALL section,price NULL NULL NULL 96734
Using
where; Using filesort
########################################
Other info:
Query cacheing = off
MySQL version = 5.0.32
OS = Debian Sarge
Sure, the second query returns 29 fewer records than the first, but
should
that make the difference in time?
Hope you can shed some light onto this :-)
Ta!
Chris.
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