Question

有人可以告诉我如何减少使用此查询的时间？

这是SQL查询：

SELECT 
    `i`.`id`, 
    `i`.`local_file`, 
    `i`.`remote_file`, 
    `i`.`remote_file_big`, 
    `i`.`image_name`, 
    `i`.`description`,
     IF(`i`.`prevent_sync`='1', '5', `i`.`status`) `status`,
     GROUP_CONCAT(`il`.`user_id` SEPARATOR ',') AS `likes`,
     COUNT(`il`.`user_id`) AS `likes_count`
FROM `images` `i`
LEFT JOIN `image_likes` `il` ON (`il`.`image_id`=`i`.`id`) 
WHERE 1 AND `i`.`created` < DATE_SUB(CURDATE(), INTERVAL 48 HOUR) 
GROUP BY `i`.`id` 
ORDER BY `likes_count` DESC LIMIT 3 OFFSET 0;

在检查查询时间时，结果如下：

# Query_time: 9.948511  Lock_time: 0.000181  Rows_sent: 3  Rows_examined: 4730490
# Rows_affected: 0

表image_likes：

id (Primary)    int(11)
local_file  varchar(100)
orig_name   varchar(100)
remote_file varchar(1000)
remote_file_big varchar(1000)
remote_page varchar(1000)   
image_name  varchar(50)
image_name_eng  varchar(50)
user_idIndex    int(11)
author  varchar(50)
credit  varchar(250)
credit_eng  varchar(250)
location    varchar(50)
description varchar(500)
description_eng varchar(275)
notes   varchar(550)
categoryIndex   int(11)
date_range  varchar(50)
createdIndex    datetime
license enum('1', '2', '3')
status  enum('0', '1', '2', '3', '4')
locked  enum('0', '1')
watch_list  enum('0', '1', '2')
url_title   varchar(100)
url_data    varchar(8192)
rem_date        datetime
rem_notes   varchar(500)
original_url    varchar(1000)
prevent_sync    enum('0', '1')
checked_by  int(11)
system_recommended  enum('0', '1')

请建议。

Answer 1

这可能会受到{inflate-deflate'综合症的影响，这种综合症经常发生在$locations=(get-azurermlocation).Location foreach ($location in $locations) { $usage=Get-AzureRmVmUsage -Location $location "Now, location is $location" |out-file D:\test1.csv -Append $usage | out-file d:\test1.csv -Append } + JOIN。此外，它通常会导致错误的聚合值。

GROUP BY

此变体将排除likes_count = 0的行，但这似乎是合理的。

它假定SELECT `id`, `local_file`, `remote_file`, `remote_file_big`, `image_name`, `description`, IF(`prevent_sync`='1', '5', `status`) `status`, s.likes, s.likes_count FROM `images` AS `i` JOIN ( SELECT GROUP_CONCAT(user_id SEPARATOR ',') AS likes, COUNT(*) AS likes_count FROM `image_likes` GROUP BY image_id ORDER BY `likes_count` DESC LIMIT 3 OFFSET 0; ) AS s ON s.`image_id`=`i`.`id` WHERE `created` < CURDATE() - INTERVAL 2 DAY ORDER BY `likes_count` DESC;的{{1}}为PRIMARY KEY。

images需要id，并会对该表进行一次扫描。然后只有3次查找到image_likes。

原始查询必须扫描INDEX(user_id)的所有行，并重复扫描所有images。

如何减少此SQL查询的时间

1 个答案: