我有一个wordpress安装，我需要在每篇帖子上查询：

select post_id, meta_key from wp_postmeta where meta_key = \'mykey\' and meta_value = \'somevalue\'

我在那张表上有300万行，查询大约需要6秒钟才能完成。我想应该快得多。如果我显示表的索引，它将返回我：

SHOW INDEX FROM wp_postmeta

Table   Non_unique  Key_name    Seq_in_index    Column_name Collation   Cardinality Sub_part    Packed  Null    Index_type  Comment Index_comment   
wp_postmeta 0   PRIMARY 1   meta_id A   3437260 NULL    NULL        BTREE       
wp_postmeta 1   post_id 1   post_id A   1718630 NULL    NULL        BTREE       
wp_postmeta 1   meta_key    1   meta_key    A   29  191 NULL    YES BTREE   

如果我做出解释，它会给我以下回复：

explain select post_id, meta_key from wp_postmeta where meta_key = \'mykey\' and meta_value = \'somevalue\'


id  select_type table   type    possible_keys   key key_len ref rows    Extra   
1   SIMPLE  wp_postmeta ref meta_key    meta_key    767 const   597392  Using where

我不太擅长mysql，所以我不知道如何检查或解决它。你能告诉我问题出在哪里吗？？

谢谢大家。

CREATE TABLE wp_postmeta (
  meta_id bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  post_id bigint(20) unsigned NOT NULL DEFAULT \'0\',
  meta_key varchar(255) DEFAULT NULL,
  meta_value longtext,
  PRIMARY KEY (meta_id),
  KEY post_id (post_id),
  KEY meta_key (meta_key)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8;

CREATE TABLE wp_postmeta (
    post_id BIGINT UNSIGNED NOT NULL,
    meta_key VARCHAR(255) NOT NULL,
    meta_value LONGTEXT NOT NULL,
    PRIMARY KEY(post_id, meta_key),
    INDEX(meta_key)
    ) ENGINE=InnoDB;

JOIN wp_postmeta AS m  ON p.id = m.post_id
WHERE m.meta_key = \'...\'