带索引的MySQL查询优化器

Question

i have a database with a lot of ads postings. it works fine when the size is small, but now the hosting company suspend my account frequently, because my database have more then 100,000 row. they told me my query is not so efficient for my table anymore. So, i did some search online, and find index might be a way to solve my query issue.

here are query for my site

$sql = "SELECT * 
        FROM `adstable` 
        WHERE `keytype` = '".$cate."' 
        ORDER BY `adstable`.`id` DESC 
        LIMIT 2000";

the $cate will change base on the category visitor select. i am using phpmyadmin, and i want to know how the index will work with the query above. I have create the index for cate column, but don't know how to optimize the query with the index i am created.

here is how i add the index

ALTER TABLE  `adstable` ADD INDEX (  `keytype` )

by using

EXPLAIN 
SELECT * 
FROM `adstable`
WHERE `keytype` = '".$cate."'
ORDER BY `adstable`.`id` DESC
LIMIT 2000

I got something like this:

id | select_type | table  | type | possible_keys | key     | key_len | ref | rows | Extra
1  | SIMPLE  |adstable| ref  | keytype       | keytype |   38    |const|49392 | Using where; Using filesort

thanks in advance.

Answer 1

If by cate column you meant keytype column , then your index is already being used. Have you noticed any improvement in the query? To check whether the index is really being used in that query you can run the following query:

EXPLAIN SELECT * FROM `adstable`
WHERE `keytype` = '".$cate."'
ORDER BY `adstable`.`id` DESC
LIMIT 2000

You can post how you created the index and the result of that query to provide more information.

Answer 2

1. Is it a MyISAM table? If yes, add a (keytype, id) index.

2. If you can lower the 2000 limit to something more sensible, eg if you don't really need 2000 rows, lower that value.

3. Do you really need all those columns in the SELECT list? If not, remove the * and write down only those columns that you need.