MySQL : Open-Source, Relational Database Management System

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Why do these two queries (which I think are equivalent) rely on different keys?

We have a query that we don't like, since it ends up doing a full table scan. EXPLAIN SELECT count(*) AS c, location.name FROM study LEFT JOIN location ON study.location_id = location.id ...
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Problem when using gtid with MySQL replication

I have faced to problem when using gtid in MySQL replication: "When @@SESSION.GTID_NEXT is set to a GTID, you must explicitly set it to a different value after a COMMIT or ROLLBACK. Please check ...
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One table for article comments, video comments and photo comments or multiple tables?

First DBA question. Greetings people. I hope I'm not duplicating a question but it's very hard finding database design related questions here (for multiple comment tables), as all 'design' questions ...
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226 views

Replication of a remote MySQL database to local MySQL database

I'm the developer of my employers corporate private website, a HTML5/PHP/CSS powered site for company reports etc. The site, hosted on a shared hosting package, connects to a remote read-only MySQL DB ...
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Randomizing the Auto Increment in Mysql

We have a database, where we insert data into table whenever we receive an order from our services. We use auto_increment to generate the ID and assign the order with the same. This is usually same ...
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MySQL getting killed by AppArmor

I have copied this link from StackOverflow as it is marked as out of topic there and is waiting to be transfered here. So, here it goes: Occasionally, without any identifiable pattern, MySQL ...
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58 views

MySQL WRITE LOCK Not Preventing Inserts

This should be a simple task. Can someone tell me why the below code is still inserting rows? lock table wp_postmeta write; insert into wp_postmeta values (null, 1,'test','test'); I've checked my ...
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Question on MySQL insert race condition

I'm using MySQL 5.1, PHP 5.3 and the table is MyISAM. Here's the DTD of this very fake table: CREATE TABLE `temp1` ( `value` varchar(10) DEFAULT NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1 This ...
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Multiple selects ordering desc from single table

I'm trying to do multiple selects to give multiple ordered columns. I'm struggling to get the below mysql query to achieve the output I want. SQLfiddle: http://www.sqlfiddle.com/#!2/a1002/3 ...
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338 views

Optimization Tips For MYSQL Tuner/Primer

So I have a site that has a crap ton of traffic. I see a decent amount of latency when the site has over 1,000 active visitors on it. I have new relic installed and it seems Im only using 10% of the ...
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Architecture for a MySQL MDBS

My coworker and I are tasked with redesigning our current Access databases in a MySQL environment. Between the two of us, this wont be a problem but we need to connect to other external databases that ...
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Is it ever a good idea to use different storage engines on MySQL for a given database?

I asked this question at http://stackoverflow.com/questions/24477834/mixing-mysql-storage-engines-in-a-database, but it was closed as being off topic. I have needs for different functionality ...
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Dealing with Multiple User Roles

I'm working on a project based on a CMS, where there is a built-in roles table. However, the CMS allows a user to have one role only using role_id And these are the requirements that struggling me: ...
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232 views

Why does this MySQL date_sub statement return wrong values?

I had a complex statement that was returning strange values and I traced it to the following line: SELECT id, updated FROM status WHERE updated > date_sub(NOW(), INTERVAL 6 MINUTE) ORDER BY ...
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364 views

“Temporary file write failure” when trying to change primary key in MySQL

In MySQL, When I trying to change primary key by this query: ALTER TABLE `resources` DROP PRIMARY KEY, ADD PRIMARY KEY (`role_id`, `category_id`, `lang`, `model`, `rule`); I execute this query ...
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Ordering a sequence of INSERT…SELECT statements to avoid a deadlock

I have the following two tables in a MySQL database: CREATE TABLE `names` ( `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(60) NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY ...
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Modulus calculation for compound primary keys in MySQL Cluster (and other sharded databases)

In MySQL Cluster, and generally in sharded databases, how is a compound primary key's modulus calculated? Say, for example, there are two tables that have primary keys like so: CREATE TABLE Orders ...
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Corrupted Filesystem: Possible to restore databases from the contents of /var/lib/mysql?

Using CentOS 6.4 x64. Not sure what happened but somehow my VPS filesystem got corrupted and it is now in a permanent read-only state. I've been working with my hosting provider's sys. admin. but ...
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MySQL replication of single DB to same server

I have a DB Server running CentOS 6.4 and MySQL 5.5 from RPMs (not source). I have dozens of databases but one of them is being hit quite hard with large selects which locks out other updates which ...
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718 views

Error when syncing MySQL database (XAMPP) on Dropbox

I'm working on a MySQL database for local development using XAMPP, and I would like to work on two different computers. Looking online, I saw this link that gives a tutorial on syncing your database ...
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How to update all primary keys in the existing database

I'm moving mysql multi-master replication to production using tungsten. I had setup the auto increment and offset values in my.cnf file. To achieve this i'll have to update my all primary keys of all ...
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Need help in optimizing a Slow Query

I am using userpoints module to provide points for different actions that they do on my site. mysql> desc userpoints; +-------------+---------+------+-----+---------+----------------+ | Field ...
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Querying number of tries since last successful log, checking IP as well as user

I asked this question before on stackoverflow, but it might fit better here, since it is mainly about database performance. The actual question With performance in mind, how would you go about ...
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71 views

Significant difference between duration for querys in SHOW PROFILE and SHOW PROFILES?

I have use mysql profiler to optimize an opencart query which takes more than 10 seconds to executes. mysql> SHOW PROFILES; ...
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MySQL dump error (#1005 - Can't create table 'novephp_cz_bv.jos_jquarks_customsets' (errno: 150))

I´m trying dump mysql database from MySQL 5.1. to MySQL 5.5. But I´m getting an error "#1005 - Can't create table 'novephp_cz_bv.jos_jquarks_customsets' (errno: 150)". Problematic part of script is ...
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Getting upcoming world wide releases from a database

From my database I want to get upcoming world wide release dates for an itemId along with the platformIds. If I have a table that looks like this and the current date is 2014-05-14 ...
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323 views

How to generate data for News Feed efficiently like facebook , googleplus , twitter e.t.c?

I have created table as post ( post_id int(15) auto_increment primary key , user_id int(11) , post_text varchar(2000) , post_type int(1), ...
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MySQL: Slow Update Queries

Our database server hangs for exactly 30 seconds on random UPDATE queries. It doesn't matter what field type the query is updating, it just seems like random selection. There are a few applications ...
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Why doesn't this query limit results by first and last name?

I have an ugly query, horrible table names courtesy of MySQL Workbench, and a severe lack of planning on my part to change to less verbose names prior to actually writing the code. Try to move past ...
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MySQL server taking up 100% CPU

I'm managing a site that does streaming video, the site is running off: Intel(R) Xeon(R) CPU E31220 @ 3.10GHz 16 GB RAM 2 x 2TB RAID1 1gbit unmetered bandwidth is not an issue as the ...
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151 views

What is a loose index scan?

I was reading that MySQL can not use an index on 2 range conditions due to not having a "loose index scan" What exactly does this mean? Is it related to the underlying or the implementation of the ...
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Table already exists error when trying to import sql file

I am trying to upload a backup sql file through phpMyAdmin. I create the empty db with the same db name as in my import file in phpMyAdmin then use the import function selected from within this empty ...
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MULTIPLE INSERT VALUES with INSERT into another table

here a scenario to have a more clear picture. The DB is MySQL. I've 2 tables events and *event_users* : EVENTS id int type int date date time time ... EVENT_USERS event_id ...
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Best database for fast read all in one table

I currently have a large database in SQLite that I was using for rapid-prototyping for a software I am working on. Now that I am planning to move it to another database that should give better ...
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Move all InnoDB databases into one subdirectory (innodb_file_per_table is ON)

First of all, excuse my English. I want to run a MySQL 5.6 on ZFS volume, and need to move all InnoDB databases to one subdirectory (which in fact will be a different ZFS filesystem). For example, by ...
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Is it possible for unique key to break master-master replication in mysql?

I have a master-master mysql setup with 2 servers running the exact same application making writes to such a table: CREATE TABLE `metric` ( `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT, ...
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What do spikes in InnoDB lock structures indicate?

I co-maintain a high traffic site similar to StackExchange. It runs MySQL 5.1 (working on replacing it with MySQL 5.5 or MariaDB). All our tables are InnoDB. MySQL goes down a couple of times a day. ...
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“dynamic set” in a MySQL table

I have a table where one column will have a few values many times (maybe 20 different values). Now I would like to use something like the set to improve performance and memory consumption. The problem ...
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1k views

Solved Mysql connection lost with HAProxy

I have master-master replication with mysql. and haproxy configured front of my master-master replication. When I connect my replication via HaProxy, mysql says that "MYSQL has gone away". But when I ...
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159 views

Master and slave tables with different character sets - will replication break?

We have some huge tables in our MySQL 5.6 database that have latin-1 as their character set, and want to convert them all to UTF-8 (along with converting the database's global character set). The ...
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Distribute records on different MySQL databases - MySQL Proxy alternative

My scenario is the following: Right now I am using one big MySQL database with multiple tables to store user data. Many tables contain auto increment columns. I would like to split this into 2 or ...
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Tagged questions

I have similar to StackExchange network that utilises tagged questions. In my web application Users also can find questions by tags. The query below returns a set of tagged questions: SELECT ...
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MySQL: Upgraded from 5.1 to 5.6 - no problem?

We're using Yum to maintain MySQL and our MySQL server only hosts a largish Drupal database. We recently upgraded via Yum from 5.1 to 5.6. The process went like so: Ran a mysqldump --all-databases ...
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crossplatform mysql_install_db script in mysql 5.5.34 on Windows

I downloaded mysql-5.5.34-win32.zip and found out there is mysql_install_db.pl script. However mysql 5.5 documentation says: mysql_install_db is a shell script and is available only on Unix ...
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Upgrading from MySQL 5.5 to 5.6 - timestamp issue?

I'm looking at upgrading my Percona Server setup from 5.5 to 5.6. Reading the upgrade docs from MySQL sounds mostly straightforward except for anything involving time/date columns. As far as I can ...
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restore using mysqlbinlog failing

While doing restore from a MySQL binary log file, it is failing with the following error . mysqlbinlog mysql-bin.000036 | mysql -u root -p asdb ERROR 1032 (HY000) at line 48: Can't find record in ...
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USING to join multiple tables with same field

I have 4 tables, each with a common field QuestionnaireId. I am wondering if there is any difference in output or performance difference between using USING on the field in each join or by specifying ...
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mysql query doesn't work inside a stored procedure

this is my stored procedure: CREATE DEFINER=`root`@`localhost` PROCEDURE `isUserValid`(IN `facebookId` VARCHAR(20), IN `userAccessToken` TEXT) NO SQL COMMENT 'check if user is valid. return ...
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How to set selinux permission for non-standard mysql bin log path?

By default, mysql bin log works in folder /var/log/mysql. but moving to any other share such /mylogs/mysql gives permission error. Below is the exact message: usr/sbin/mysqld: File ...
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mysql database is corrupt after system power failure

I have mysql database using xampp in my widows system. its got currupt after power failure i have back of database before 2 days but i dont have backup of one day transactions. now i tried ...