mysql索引使組緩慢

Question

請參閱下面的表strcuture。

CREATE TABLE `oarc` (
    `ID` bigint(20) NOT NULL AUTO_INCREMENT, 
    `zID` int(11) NOT NULL, 
    `cID` int(11) NOT NULL, 
    `bID` int(11) NOT NULL, 
    `rtype` char(1) COLLATE utf8_unicode_ci NOT NULL, 
    `created` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00', 
    PRIMARY KEY (`ID`) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=1821039 ; 

除PRIMARY KEY，我沒有設置任何這指數，當我運行下面的查詢

select COUNT(oarc.ID) as total 
    from `oarc` where`oarc`.`rtype` = 'v' 
group 
    by `oarc`.`zID` 

我得到的結果在不到1秒。但是，如果我將索引添加到zID，則需要超過5秒。

請參見下面的解釋結果：

id | select_type | table | type | possible_keys | key  | key_len | ref  | row  | Extra 
-------------------------------------------------------------------------------------------------------- 
1 | SIMPLE  | oarc | index | NULL   | zone_ID | 4  | NULL  | 1909387 | Using where 

目前該表已超過1821039個記錄它，它會每小時的基礎上增加。爲了減少查詢執行時間，我需要做哪些事情？我只希望在表和查詢級別有一些東西，my.cnf或服務器端沒有，因爲我在那裏什麼都做不了。

在此先感謝。

Answer 1

這樣比較好嗎？

CREATE TABLE `oarc` (
    `ID` bigint(20) NOT NULL AUTO_INCREMENT, 
    `zID` int(11) NOT NULL, 
    `cID` int(11) NOT NULL, 
    `bID` int(11) NOT NULL, 
    `rtype` char(1) COLLATE utf8_unicode_ci NOT NULL, 
    `created` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00', 
    PRIMARY KEY (`ID`), 
    KEY(rtype,zid) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=1821039 ; 

explain 
select COUNT(oarc.ID) as total 
    from `oarc` where`oarc`.`rtype` = 'v' 
group 
    by `oarc`.`zID` 

+----+-------------+-------+------+---------------+-------+---------+-------+------+--------------------------+ 
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra     | 
+----+-------------+-------+------+---------------+-------+---------+-------+------+--------------------------+ 
| 1 | SIMPLE  | oarc | ref | rtype   | rtype | 3  | const | 1 | Using where; Using index | 
+----+-------------+-------+------+---------------+-------+---------+-------+------+--------------------------+