"Mojtaba Faridzad" <[EMAIL PROTECTED]> 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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