>"Mojtaba Faridzad" <mfaridzad@stripped> wrote:
> > I'm learning MySQL and I got two question:
> >
> > 1) As I know, MySQL has a buffer to keep the last records which have
>been retreived. So if I run a query two times, the second time will be
>faster. How can I temporarly stop this service? because I want to run
>different queries and compare their speed and find the best solution for a
>problem.
In newer versions of mysql (4.0.3+), you can issue
set global query_cache_limit=0;
in older versions, you need to set the value in my.cnf, then restart the
server.
> > 2) A table has 2 fields, Active CHAR(1), and Company CHAR(40). Sometimes
>I want to search a company name and sometimes I want to search an active
>company. For faster searching, do I need to create two index like these:
> > CREATE INDEX active ON customer (CONCAT(active, company));
No need to specify "concat"
CREATE INDEX ative ON customer (active, company)
should do.
> > CREATE INDEX company ON customer (company);
> >
> > If I create just the first index, do I still have a fast searching on
>company name ( without mentioning Active )? like this:
> > SELECT * FROM customer WHERE company = 'my test company';
>
>Nope. If you have index only on (active, company), it will not be used in
>the above query.
True.
- Rich
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