MySQL Select查询执行缓慢
我有以下疑问MySQL Select查询执行缓慢,mysql,performance,pdo,Mysql,Performance,Pdo,我有以下疑问 SELECT DISTINCT * FROM vPAS_Posts_Users WHERE (post_user_id =:id AND post_type != 4) AND post_updated >:updated GROUP BY post_post_id UNION SELECT DISTINCT vPAS_Posts_Users.* FROM PAS_Follow JOIN vPAS_Posts_Users ON ( PAS_Follow.fol
SELECT DISTINCT * FROM
vPAS_Posts_Users
WHERE (post_user_id =:id AND post_type != 4)
AND post_updated >:updated
GROUP BY post_post_id
UNION
SELECT DISTINCT vPAS_Posts_Users.* FROM PAS_Follow
JOIN vPAS_Posts_Users ON
( PAS_Follow.folw_followed_user_id = vPAS_Posts_Users.post_user_id )
WHERE (( PAS_Follow.folw_follower_user_id =:id AND PAS_Follow.folw_deleted = 0 )
OR ( post_type = 4 AND post_passed_on_by = PAS_Follow.folw_follower_user_id
AND post_user_id !=:id ))
AND post_updated >:updated
GROUP BY post_post_id ORDER BY post_posted_date DESC LIMIT :limit
：id=7：updated=0.0：limit=40CREATE ALGORITHM=UNDEFINED DEFINER=`MySQLUSer`@`%` SQL SECURITY DEFINER VIEW `vPAS_Posts_Users`
AS SELECT
`PAS_User`.`user_user_id` AS `user_user_id`,
`PAS_User`.`user_country` AS `user_country`,
`PAS_User`.`user_city` AS `user_city`,
`PAS_User`.`user_company` AS `user_company`,
`PAS_User`.`user_account_type` AS `user_account_type`,
`PAS_User`.`user_account_premium` AS `user_account_premium`,
`PAS_User`.`user_sign_up_date` AS `user_sign_up_date`,
`PAS_User`.`user_first_name` AS `user_first_name`,
`PAS_User`.`user_last_name` AS `user_last_name`,
`PAS_User`.`user_avatar_url` AS `user_avatar_url`,
`PAS_User`.`user_cover_image_url` AS `user_cover_image_url`,
`PAS_User`.`user_bio` AS `user_bio`,
`PAS_User`.`user_telephone` AS `user_telephone`,
`PAS_User`.`user_dob` AS `user_dob`,
`PAS_User`.`user_sector` AS `user_sector`,
`PAS_User`.`user_job_type` AS `user_job_type`,
`PAS_User`.`user_unique` AS `user_unique`,
`PAS_User`.`user_deleted` AS `user_deleted`,
`PAS_User`.`user_updated` AS `user_updated`,
`PAS_Post`.`post_post_id` AS `post_post_id`,
`PAS_Post`.`post_language_id` AS `post_language_id`,
`PAS_Post`.`post_type` AS `post_type`,
`PAS_Post`.`post_promoted` AS `post_promoted`,
`PAS_Post`.`post_user_id` AS `post_user_id`,
`PAS_Post`.`post_posted_date` AS `post_posted_date`,
`PAS_Post`.`post_latitude` AS `post_latitude`,
`PAS_Post`.`post_longitude` AS `post_longitude`,
`PAS_Post`.`post_location_name` AS `post_location_name`,
`PAS_Post`.`post_text` AS `post_text`,
`PAS_Post`.`post_media_url` AS `post_media_url`,
`PAS_Post`.`post_image_height` AS `post_image_height`,
`PAS_Post`.`post_link` AS `post_link`,
`PAS_Post`.`post_link_title` AS `post_link_title`,
`PAS_Post`.`post_unique` AS `post_unique`,
`PAS_Post`.`post_deleted` AS `post_deleted`,
`PAS_Post`.`post_updated` AS `post_updated`,
`PAS_Post`.`post_original_post_id` AS `post_original_post_id`,
`PAS_Post`.`post_original_type` AS `post_original_type`,
`PAS_Post`.`post_passed_on_by` AS `post_passed_on_by`,
`PAS_Post`.`post_passed_on_caption` AS `post_passed_on_caption`,
`PAS_Post`.`post_passed_on_fullname` AS `post_passed_on_fullname`,
`PAS_Post`.`post_passed_on_avatar_url` AS `post_passed_on_avatar_url`
FROM (`PAS_User` join `PAS_Post` on((`PAS_User`.`user_user_id` = `PAS_Post`.`post_user_id`)));
SELECT *
FROM
vPAS_Posts_Users
WHERE
post_user_id =:id
AND post_type != 4
AND post_updated > :updated
UNION
SELECT u.*
FROM vPAS_Posts_Users u
JOIN PAS_Follow f ON f.folw_followed_user_id = u.post_user_id
WHERE
u.post_updated > :updated
AND ( (f.folw_follower_user_id = :id AND f.folw_deleted = 0)
OR (u.post_type = 4 AND u.post_passed_on_by = f.folw_follower_user_id AND u.post_user_id != :id)
)
ORDER BY u.post_posted_date DESC;
LIMIT :limit
其他改进 索引： 确保在以下列上有索引：
- PAS_User.User_User_id
- PAS\U Post.Post\U用户\U id
- PAS_Post.Post_类型
- PAS_Post.Post_更新
- PAS_Follow.Follow_Follow_用户id
- PAS_Follow.folw_已删除
- 通过了
解释结果
从您的解释中，我可以看出，您的大多数表除了主表外没有任何键，我建议您在要加入的列上添加一些额外的键，例如：PAS_Follow.folw_followerd_user_id和vPAS_Posts_Users.post_user_id，这将大大提高性能 再见，
Gnagno以下是一些关于查询和查看的建议，首先对两个结果集使用
UNIONUNION allUNION ALLUNIONUNIONUNION ALLUNION ALLUNIONDISTINCT中使用的列，其中，ORDER BY、GROUP BYpost_posted_dateSELECT q.* FROM (
SELECT * FROM
vPAS_Posts_Users
WHERE (post_user_id =:id AND post_type != 4)
AND post_updated >:updated
UNION ALL
SELECT vPAS_Posts_Users.* FROM PAS_Follow
JOIN vPAS_Posts_Users ON
( PAS_Follow.folw_followed_user_id = vPAS_Posts_Users.post_user_id
AND vPAS_Posts_Users.post_updated >:updated)
WHERE (( PAS_Follow.folw_follower_user_id =:id AND PAS_Follow.folw_deleted = 0 )
OR ( post_type = 4 AND post_passed_on_by = PAS_Follow.folw_follower_user_id
AND post_user_id !=:id ))
) q
GROUP BY q.post_post_id ORDER BY q.post_posted_date DESC LIMIT :limit
您能告诉我为什么需要distinct*，这个表中有多少字段，我会说将它限制在您想要的字段中，这样可以稍微改进查询。此外，为什么您需要一个group by和一个distinct，这样做有特定的目的吗？总之，不，我多次构建查询以获得我想要的结果，但我没有真正关注这一点，这会导致问题吗？这里有很多麻烦，可能会使您的查询性能不佳。首先，不要使用
选择*selectdistinct*分组依据或