On Mon, 30 Apr 2001, ryc wrote:
> I have a fairly large table (greater than 4mil rows) that I would to preform
> a query like:
>
> SELECT col1,col2 FROM table WHERE a=1, c=2 ORDER BY b DESC LIMIT 50;
>
> I have an index on the table INDEX1( a,b,c );
>
> When running the query as is, it takes around 4seconds. If I omit the "DESC"
> part the query runs in a fraction of a second.
>
> I would like the query to run faster when I use DESC. I looked at
> myisamchk -R to sort by the 'b' index but I want to be sure it will speed up
> my query since it may take a while to sort all 4million rows.
To improve things I'd suggest you drop the (a,b,c) index and create two new ones:
one on (a,c)
and another on (b)
and then do the myisamchk -R on the second index
You might also consider the --sort-records=# option
regards,
thalis
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