MySQL most faster results with indexes - mysql

Question

I have the following structure with indexes that help us to retrieve faster:
CREATE TABLE IF NOT EXISTS `index_site` ( `id_building` char(32) NOT NULL, `id_client` char(32) NOT NULL, `id_broker` smallint(5) unsigned NOT NULL, `kind_client` char(1) NOT NULL, `city` smallint(6) unsigned NOT NULL, `lat` float(10,6) NOT NULL, `lng` float(10,6) NOT NULL, `zone` smallint(2) unsigned NOT NULL, `sector` smallint(4) unsigned NOT NULL, `subregion` smallint(6) unsigned NOT NULL, `country` char(2) NOT NULL, `habs` smallint(5) unsigned NOT NULL, `bath` smallint(5) unsigned NOT NULL, `persons` smallint(5) unsigned NOT NULL, `include_elevator` enum('1','0') NOT NULL, `build_level` varchar(20) NOT NULL, `area` mediumint(8) unsigned NOT NULL, `area_um` enum('1','2','3','4','5') NOT NULL, `area_str` varchar(10) NOT NULL, `code` char(10) NOT NULL, `title` tinytext NOT NULL, `type_offer` varchar(50) NOT NULL, `offer_name` varchar(20) NOT NULL, `comments` text NOT NULL, `type_building` varchar(50) NOT NULL, `address` tinytext NOT NULL, `sector_name` tinytext NOT NULL, `city_name` varchar(50) NOT NULL, `subregion_name` varchar(50) NOT NULL, `area_terrain` varchar(10) NOT NULL, `area_um_terrain` tinyint(4) NOT NULL, `image` varchar(70) NOT NULL, `image_total` tinyint(2) unsigned NOT NULL, `build_status` tinyint(3) unsigned NOT NULL, `tags` text NOT NULL, `url` varchar(200) NOT NULL, `include_offer_value` enum('1','0') NOT NULL, `offer_value` varchar(15) NOT NULL, `offer_value_format` varchar(20) NOT NULL, `prc_comission` varchar(5) NOT NULL, `date_added` datetime NOT NULL, `date_updated` datetime NOT NULL, `date_expire` datetime NOT NULL, `date_suspended` date NOT NULL, `visits` int(11) NOT NULL, `kind_offer` tinyint(4) NOT NULL, `kind_building` tinyint(5) unsigned NOT NULL, `kind_building_type` tinyint(5) unsigned NOT NULL, `mark_bld` tinyint(3) unsigned NOT NULL, `mark_bld_color` char(7) NOT NULL, `status` tinyint(1) unsigned NOT NULL, `is_made` enum('0','1') NOT NULL, `is_project` enum('0','1') NOT NULL, `is_bm` enum('0','1') NOT NULL, `is_demo` enum('0','1') NOT NULL, `is_leading` enum('0','1') NOT NULL, `visible_in_metasearch` mediumtext NOT NULL, `visible_in_web` mediumtext NOT NULL, `seller_image` varchar(150) NOT NULL, `seller_name` varchar(50) NOT NULL,
KEY `id_broker` (`id_broker`), KEY `id_client` (`id_client`), KEY `kind_building` `kind_building`), KEY `city` (`city`), KEY `offer_value` (`offer_value`), KEY `is_bm` (`is_bm`), KEY `status` (`status`), KEY `sector` (`sector`), KEY `zone` (`zone`), KEY `area` (`area`), KEY `prc_comission` (`prc_comission`), KEY `is_made` (`is_made`), KEY `is_leading` (`is_leading`), KEY `id_building` (`id_building`), KEY `date_added` (`date_added`), KEY `code` (`code`), KEY `country` (`country`), KEY `habs` (`habs`), KEY `kind_offer` (`kind_offer`), FULLTEXT KEY `tags` (`tags`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 ROW_FORMAT=FIXED;
Yes, it's too big!!! :)
Okay, the topic is in structure I use some keys when I find results; this is normal and I execute the following query:
SELECT * FROM `index_site` WHERE kind_building='1' AND kind_offer='1' AND city='1'
This query took 0.0179 seconds, great, but I add EXPLAIN to my query:
EXPLAIN SELECT * FROM `index_site` WHERE kind_building='1' AND kind_offer='1' AND city='1'
I got the following result:
+----+-------------+------------+-------------+-------------------------------+-------------------------------+---------+------+------+-------------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+-------------+-------------------------------+-------------------------------+---------+------+------+-------------------------------------------------------------+
| 1 | SIMPLE | index_site | index_merge | kind_building,city,kind_offer | kind_offer,city,kind_building | 1,2,1 | NULL | 184 | Using intersect(kind_offer,city,kind_building); Using where |
+----+-------------+------------+-------------+-------------------------------+-------------------------------+---------+------+------+-------------------------------------------------------------+
And I use the right keys but in the column Extra by MySQL when I get "Using where" they say that "you look something is wrong".
My question is, if I have a correct query with indexes, What is the problem to get "Using where" Whats wrong?
Thanks for your help!

Answer 1

From the docs:
If the Extra column also says Using where, it means the index is being used to perform lookups of key values.
You are selecting all fields (*) from the table.
Since not all fields are covered by indexes used in the merge intersect, the fields need to be looked up in the table itself.
Try running this:
SELECT kind_building, kind_offer, city
FROM index_site
WHERE kind_building = '1'
AND kind_offer = '1'
AND city = '1'
, and Using where should go.