mysql

Mysql, is ther an easy way to create a table with 500000 (dummy/zero/empty) rows [closed]

由 為{幸葍}努か 提交于 2021-02-11 15:30:03
问题 Closed . This question needs to be more focused. It is not currently accepting answers. Want to improve this question? Update the question so it focuses on one problem only by editing this post. Closed 5 years ago . Improve this question I've been working with sql databases just for a little time but I'm impressed of the powerful possibilities that I discovered so far. Now I want to do something that sounds so easy but I was not able to find an easy way to solve it: Just create a new table

Explanation of PDO IN clause using prepared statements

由 我与影子孤独终老i 提交于 2021-02-11 15:21:29
问题 I am reading this answer: PHP - Using PDO with IN clause array It uses the code: $in_array = array(1, 2, 3); $in = str_repeat('?,', count($in_array) - 1) . '?'; $sql = "SELECT * FROM my_table WHERE my_value IN ($in)"; $stm = $db->prepare($sql); $stm->execute($in_array); $data = $stm->fetchAll(); Can anyone explain why they used $in = str_repeat('?,', count($in_array) - 1) . '?'; instead off: $in = str_repeat('?,', count($in_array)); I am puzzled and cannot figure out the logic behind the

SQL get all of the users last search

由 半城伤御伤魂 提交于 2021-02-11 15:02:35
问题 I can easily get the users searches, but I would like to get all of the users LAST search. For example, the SQL code below will get this specific users last search. select uid, itemDescription, date from SEARCH WHERE date BETWEEN '2020-03-01' AND '2020-03-30' AND uid = "000-000-000-000-000" ORDER BY date DESC LIMIT 1 If I try to edit this and remove the uid = "" , this wont work since it will limit to one search. If I remove the LIMIT 1 also and add a GROUP BY uid , its not picking up the

Mysql Add another table into Join

由 孤街醉人 提交于 2021-02-11 14:54:15
问题 i have a table i would like to add to my current Join: Table ( report_images ) include a report_id and a image_path . Reference: Mysql Inner Join and Group By repeating row How it is now: ["text": "My first report", user: [{"display_name": "Cyclops", "photo_url": "CYCLOPS_IMAGE.png"}], comments: [{"text": "Great Report", display_name: "Xavier"}, {"text": "Bad Report", display_name: "Logan"}, {"text": "Thanks for the feedback", display_name: "Cyclops"}]] What i expect: ["text": "My first

I want to delete duplicate rows from my database table

由 ☆樱花仙子☆ 提交于 2021-02-11 14:53:28
问题 I went through a few answers on this topic but none of them are executing on my workbench. I have duplicate rows in my table and I want to delete all retaining only one of them. First I grouped them by Count function and then tried deleting them but it isn't working. I tried running CTE query from old questions on the website: WITH ReferenceDP AS ( SELECT[ReferenceId1], row_number() OVER(PARTITION BY ReferenceId1 ORDER BY ReferenceId1) AS [rn] FROM TABLE ) DELETE ReferenceDP WHERE [rn] > 1

Page Redirecting issues Node-js

由 ≯℡__Kan透↙ 提交于 2021-02-11 14:48:28
问题 I'm trying to open places.ejs file on clicking the submit button on show.js page, just like the show.ejs page opens on clicking the submit button on new.ejs file, but a reference error is occurring. Please help me fix the error. I'm attaching herewith my routes.js code and a part of my index.js code Any help would be highly appreciable. Thank you routes.js const { con, sessionStore } = require('./config/db'); exports.new = function(req, res){ message = ''; if(req.method == "POST"){ const post

MySQL : Selecting the rows with the highest group by count

由 末鹿安然 提交于 2021-02-11 14:46:24
问题 i have a table with records that are updated every minute with a decimal value (10,2). To ignore measure errors i want to have the number that has been inserted the most. Therefor i tried : SELECT date_time,max(sensor1),count(ID) FROM `weigh_data` group by day(date_time),sensor1 This way i get the number of records ` Datetime sensor1 count(ID) 2020-03-19 11:49:12 33.22 3 2020-03-19 11:37:47 33.36 10 2020-03-20 07:32:02 32.54 489 2020-03-20 00:00:43 32.56 891 2020-03-20 14:20:51 32.67 5 2020

面试官问你MySQL的优化，看这篇文章就够了

由 血红的双手。 提交于 2021-02-11 14:43:54
一、EXPLAIN 做MySQL优化，我们要善用 EXPLAIN 查看SQL执行计划。 下面来个简单的示例，标注(1,2,3,4,5)我们要重点关注的数据 type列，连接类型。一个好的sql语句至少要达到range级别。杜绝出现all级别 key列，使用到的索引名。如果没有选择索引，值是NULL。可以采取强制索引方式 key_len列，索引长度 rows列，扫描行数。该值是个预估值 extra列，详细说明。注意常见的不太友好的值有：Using filesort, Using temporary 二、SQL语句中IN包含的值不应过多 MySQL对于IN做了相应的优化，即将IN中的常量全部存储在一个数组里面，而且这个数组是排好序的。但是如果数值较多，产生的消耗也是比较大的。再例如： select id from table_name where num in(1,2,3) 对于连续的数值，能用 between 就不要用 in 了；再或者使用连接来替换。 三、SELECT语句务必指明字段名称 SELECT *增加很多不必要的消耗（cpu、io、内存、网络带宽）；增加了使用覆盖索引的可能性；当表结构发生改变时，前断也需要更新。所以要求直接在select后面接上字段名。 四、当只需要一条数据的时候，使用limit 1 这是为了使EXPLAIN中type列达到const类型 五

AWS EB undefined RDS_HOSTNAME with Database hosts array empty

由 百般思念 提交于 2021-02-11 14:40:02
问题 Currently in a Laravel project using AWS EB with RDS. When I run php artisan migrate --seed then I get PHP Notice: Undefined index: RDS_HOSTNAME in /var/app/current/config/database.php on line 5 PHP Notice: Undefined index: RDS_USERNAME in /var/app/current/config/database.php on line 6 PHP Notice: Undefined index: RDS_PASSWORD in /var/app/current/config/database.php on line 7 PHP Notice: Undefined index: RDS_DB_NAME in /var/app/current/config/database.php on line 8 and Database hosts array is
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