mysql - 如何优化我的查询？

Question

我编写了一个查询来从 WordPress 数据库中提取报告。查询速度慢得令人难以置信，所以我想优化它。我做了一些研究，但无法理解加快查询速度的最佳方法是什么(即使我写了，我也几乎不明白我做了什么。)有人可以指出我优化这个的正确方向吗？查询速度慢。

SELECT
wp1.meta_value as firstName,
wp2.meta_value as middleName,
wp3.meta_value as lastName,
wp5.meta_value as email2,
wp6.meta_value as address,
wp7.meta_value as city,
wp8.meta_value as state,
wp9.meta_value as zip,
wp10.meta_value as country,
wp11.meta_value as phone,
wp12.meta_value as dateOfBirth
FROM wp99_usermeta wp1
JOIN wp99_usermeta wp2 ON wp1.user_id = wp2.user_id and wp2.meta_key = 'middle_name'
JOIN wp99_usermeta wp3 ON wp1.user_id = wp3.user_id and wp3.meta_key = 'last_name'
JOIN wp99_usermeta wp5 ON wp1.user_id = wp5.user_id and wp5.meta_key = 'email2'
JOIN wp99_usermeta wp6 ON wp1.user_id = wp6.user_id and wp6.meta_key = 'street_address'
JOIN wp99_usermeta wp7 ON wp1.user_id = wp7.user_id and wp7.meta_key = 'city'
JOIN wp99_usermeta wp8 ON wp1.user_id = wp8.user_id and wp8.meta_key = 'state'
JOIN wp99_usermeta wp9 ON wp1.user_id = wp9.user_id and wp9.meta_key = 'zip'
JOIN wp99_usermeta wp10 ON wp1.user_id = wp10.user_id and wp10.meta_key = 'country'
JOIN wp99_usermeta wp11 ON wp1.user_id = wp11.user_id and wp11.meta_key = 'phone'
JOIN wp99_usermeta wp12 ON wp1.user_id = wp12.user_id and wp12.meta_key = 'date_of_birth'
WHERE wp1.meta_key = 'first_name' 

默认的wp_usermeta表结构:

CREATE TABLE `wp_usermeta` (
  `umeta_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `user_id` bigint(20) unsigned NOT NULL DEFAULT '0',
  `meta_key` varchar(255) DEFAULT NULL,
  `meta_value` longtext,
  PRIMARY KEY (`umeta_id`),
  KEY `user_id` (`user_id`),
  KEY `meta_key` (`meta_key`)
) ENGINE=***  DEFAULT CHARSET=utf8 AUTO_INCREMENT=15 ;

尝试 ALTER TABLE 建议。这在第 5 行给了我一个错误

更改表 wp99_usermeta 添加索引meta_key__user_id (meta_key, user_id) ;

SELECT
wp1.meta_value as firstName,
wp2.meta_value as middleName,
wp3.meta_value as lastName,
wp5.meta_value as email2,
wp6.meta_value as address,
wp7.meta_value as city,
wp8.meta_value as state,
wp9.meta_value as zip,
wp10.meta_value as country
FROM wp99_usermeta wp1
JOIN wp99_usermeta wp2 ON wp1.user_id = wp2.meta_key__user_id = 'middle_name'
JOIN wp99_usermeta wp3 ON wp1.user_id = wp3.meta_key__user_id = 'last_name'
JOIN wp99_usermeta wp5 ON wp1.user_id = wp5.meta_key__user_id = 'email2'
JOIN wp99_usermeta wp6 ON wp1.user_id = wp6.meta_key__user_id = 'street_address'
JOIN wp99_usermeta wp7 ON wp1.user_id = wp7.meta_key__user_id = 'city'
JOIN wp99_usermeta wp8 ON wp1.user_id = wp8.meta_key__user_id = 'state'
JOIN wp99_usermeta wp9 ON wp1.user_id = wp9.meta_key__user_id = 'zip'
JOIN wp99_usermeta wp10 ON wp1.user_id = wp10.meta_key__user_id = 'country'
WHERE wp1.meta_key = 'first_name' 

Answer 1

您可以使用GROUP BY尝试一些乐趣:

SELECT
  MAX( IF( meta_key = 'first_name', meta_value , NULL ) AS firstName,
  MAX( IF( meta_key = 'last_name',  meta_value , NULL ) AS lastName,
  ...
FROM wp99_usermeta
GROUP BY user_id

如果您必须过滤实体，您可以执行类似的操作:

SELECT
  MAX( IF( b.meta_key = 'first_name', b.meta_value , NULL ) AS firstName,
  MAX( IF( b.meta_key = 'last_name',  b.meta_value , NULL ) AS lastName,
  ...
FROM wp99_usermeta a
JOIN wp99_usermeta b
WHERE a.meta_key = 'first_name'
  AND a.meta_value = 'Joe'
GROUP BY user_id