MySQL : Open-Source, Relational Database Management System

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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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2answers
54 views

When do I need transactions /locks?

I know that transactions are meant to group several operations as one. But if for example in the same table one transaction does DELETE FROM table where state = 'done' and another does either SELECT ...
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29 views

Why does the delete/update block each other in this case?

The following drives me crazy. I have: session1>begin; session2>begin; session2>update dummy set salary=1000 where id=11; session1>delete from dummy where id=1; id is the PK ...
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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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Big Mysql table optimization

I have a table that I use to cache google translate API answers. Table structure is orig_string and group are indexes Now it has more that 1million rows with 35000 distinct values in group field. ...
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1answer
25 views

MySQL performance issues when saving Bitcoin data

I have set a cron job to a php script which periodically checks Bitcoin for new blocks, and if there are any, add the blocks and transactions to a database. After a few million records have been ...
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29 views

How can I execute multiple statements at once in MySQL Workbench?

I'm trying to execute multiple LOAD DATA INFILE statements at once using MySQL Workbench. However, they execute one at a time. Anyway of forcing them to run in parallel? Thanks for the help!
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39 views

How to verify data dumps between two MS SQL and MySQL

I'm trying to verify data exported from MSSQL and imported into MySQL is 100% accurate using MD5 hash. On Linux, I'm using md5sum and WinMD5 on Windows. The encoding is the same: UTF8. I tried both ...
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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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3answers
45 views

How to repair, or drop/create a corrupted table in mysql?

Situation: I have a MySQL database with 104 tables, running locally on XAMPP on windows 7. All the tables have InnoDB engine. XAMPP MySQL is running as windows service. As front end I have PHP ...
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1answer
40 views

Large RAM use after import database - ubuntu server

My new vps has 4 GB of RAM. Before importing database system use about 1,2 GB of RAM. When I import database, about 250 MB sql file, 25000 tables use of RAM goes to 97%. Htop showing 3302 mb in cache. ...
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1answer
26 views

MySQL update row cell with 0 value with value from closest row that does not have 0 value

I have a list of entries that has a time field where unix timestamp is stored. I recently discovered that some of the entries have that field value 0. I want to run an update that will update those ...
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1answer
23 views

What happens when CREATE INDEX gets interrupted (manually or accidentally)?

It takes hours or even days to create an index for a table of millions of rows. What happens to the database / data when CREATE INDEX gets interrupted? Such as when I manually used Ctrl-C or when ...
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1answer
41 views

Slow MySql server - even on a super fast server

I have just upgraded my 12 year old server to a really fast new one. It is a dedicated server, Dell R620 1 x Intel E5-2620 (2.0GHz, 6C) CPU 32GB RAM - 4 x 250GB SSD RAID 1, in short vastly faster in ...
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1answer
39 views

how to update date field in a record to null?

I have records in a table which a field named as 'validity' contains date as '8/15/1947 12:00:00 AM'. I need to set this date as null. I am having 1000 records,in that validity field is '8/15/1947 ...
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1answer
27 views

copy table comments from one MySQL database to another

I wrote column comments in MySQL database replica made for testing. Now I need to copy these comments to production database. Since comments are stored in table COLUMNS of information_schema database, ...
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1answer
43 views

limiting rows in joins

So I have this problem with one of my queries. The query is meant to get data from table patients and join the table patient_nurse, then table nurses to it. The patients table is as follows id | ...
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2answers
54 views

Why Can't I find my databases from Mysql on linux?

I'm new to linux. I cannot get a list of my databases by typing SHOW DATABASES on the MySQL shell. Though this MySQL program is aware of the MySQL datadir because it is listed when I type SHOW ...
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1answer
19 views

Is it possible to group by a fraction of the result set?

I have a database of products with prices. What I'd like to be able to do is figure out 5 different price ranges such that each range, when ordered by price, will have approximately the same number of ...
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2answers
71 views

Problem translating MySQL to PostgreSQL

We're using Trac for issue tracking. I migrated it from MySQL to PostgreSQL, but some of the ticket queries no longer work. In the below, all I did this far is replace IFNULL() with COALESCE() and ...
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30 views

MySQL - How to get multiple/batch averages from daily data

I'm really not sure how to tackle this so let me explain my goal... Lets say I have 30 people that enter a piece of information into a table and let's also say that 20 of these people do this between ...
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1answer
37 views

MySQL Rows to Columns to HBase (using Sqoop)

I have a table that looks like this in MySQL: id | date | num | avg I have found that I can use this for rows to columns and it works so far: SELECT CONCAT(id, '-', date), MAX(IF(`num` = ...
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2answers
29 views

MySQL timestamp timezone handling

Does the timestamp data type represent an instant-in-time or a year-month-date-hour-minute-second value? An instant in time is a moment, like the moment you started reading this, and it can be ...
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MySQL password is changed automatically

I'm the lone user of my computer. I haven't changed my MYSQL root user password, but it is somehow changed to empty password. Help me out ! My default sakila db is also gone. I specified ...
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2answers
437 views

A little clarification on how 'LIMIT' works

Not being a full blooded member of the DBA clan, but more of a dev clan, I find myself trying to figure out some slow running queries. The subject of my question however is not 'Why my queries are ...
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34 views

How to create an Access query to find # symbol into a field?

It seems easy but I'm missing something. I have a MySQL database that is connected from access through ODBC connector. I'm looking for the fields where there are # symbol but I'm getting zero ...
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1answer
34 views

Last used index from specific table

how can i take last used index from a specific table and add a +1 to it? database login, table cars I think i need to add it here #### $sql = 'INSERT INTO '.$this->options['db_table'] ...
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2answers
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Is there a rule of thumb regarding the size and number of a buffer pool instances?

I know the consensus seems to be approximately 75% of ram should be dedicated to the buffer pool. But, I'm more interested in the optimal number of buffer pool instances. What are some things to ...
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MySQL: How to calculate potential wait time?

I'm trying understand the relationship between WAIT_MS and COUNT_STAR. Is this saying the average wait time is 3.2s and occurred 11,543 times for a total of approximately 10.5hrs of aggregate wait ...
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1answer
51 views

Why is this query slow, it seems simple

I have a very typical table of user information for my application, with an average set of columns (ints, varchars, etc). In this table are two varchar(100) fields: emailAddress and emailAddress2. ...
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1answer
16 views

Is it possible to recover from a LOST_EVENTS incident from an RDS read replica?

I was setting up a read replica of an RDS database for a reporting project, and issued an incorrect GRANT statement when configuring a user. My RDS read replica stopped, with an error message on the ...
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1answer
31 views

Restore InnoDB from .frm files

My database crashed and my PC and I now only have the .frm and .ibd files left. Is there any way to restore my database?
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26 views

How do I fix Replication event checksum verification failed while reading from network. Error_code: 1743

Our server had disk space problems. As a result, replication's IO Threads fails to start. Here are the errors in mysql error log: [Note] Slave I/O thread: connected to master ...
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17 views

Adding ID in second Table

I have two table one is photos and another one is photo_detail, this is how i have created both tables: /* creating photos table */ CREATE TABLE photos( -> pid INT(10) NOT NULL AUTO_INCREMENT, ...
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1answer
24 views

How to overwrite csv file of MySQL result set?

My SQL query is given below, select company.Company_name as COMPANY_NAME, IFNULL(followup.contact_date, ' ') AS FOLLOW_UP_DATE, IFNULL((select Full_name from user where user_id = followup.user_id), ...
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1answer
25 views

MySQL multi-source replication with identical DB names

How can I set up a multi-source master/slave relation with masters having the same database names? I am using the MySQL labs 5.7.2 release with multi-source replication. One of the use cases for ...
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Optimizing MySQL query

I have a Sql query to optimize, its execution time is 8.5 Sec. I have made index on fields (timesheetdate,deleted) and able to reduce execution time to 8 Sec. A behavior I noticed that when I change ...
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1answer
17 views

MySQL: Prevent DROP TABLE and TRUNCATE TABLE on Slaves

Can someone tell me how to prevent the following commands DROP TABLE <tbl-name>; TRUNCATE TABLE <tbl-name>; from being replicated to slaves?
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50 views

Get only future records

I have the following query: SELECT master.master_id, master.showname, MIN(CONCAT(shows.show_date, ' ', shows.show_time)) AS first_show_date, MAX(CONCAT(shows.show_date, ' ', shows.show_time)) AS ...
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1answer
24 views

merge rows based on column

I have attendance_log table : +----------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | ...
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1answer
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mysql - Waiting for table level lock on a table

I have a problem with my website.. The last few days, at random times the website has become very slow. I started to investigate the best I could. I saw that the MySQL process was using 85 - 95% of ...
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1answer
17 views

MyISAM recover updated row

The row (with type MEDIUMTEXT) has been accidentally updated with empty value. I can see previous data in MYD file of a table, but I can't get them neither from mysqldump or any mysql client. If I ...
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1answer
50 views

LOAD DATA INFILE decline in performance

Query for insert: LOCK TABLE tbl WRITE; ALTER TABLE tbl DISABLE KEYS; load data local infile "E:/One.txt" into table tbl fields terminated by "\t" lines terminated by "\n" (user_id, sexid, cityid); ...
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MySQL Replication with Tungsten

I am trying to setup a multi-master type of replication with each master having an additional slave using tungsten. As an example, lets say I have 4 hosts (A,B,C,D) and Hosts A and C are the Masters, ...
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1answer
38 views

Amazon RDS mysqbinlog “Could not find first log file name in binary log index file”

Preamble: We use RDS at AWS to manage our MySQL database. I know that RDS creates binary logs used for replication.. I want to harvest these binary logs and store them on S3, so that at any time, i ...
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17 views

Get categorie, subcategories and number of products assigned to each

I have a list of products, and a list of categories, and a join table. Products can be assigned to multiple categories. Categories can have one level of subcategories. The tables look something like ...
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1answer
41 views

update variable from multiple tables in one row

I have two databases, and I need to UPDATE variable 'birthday' from one row to another checking 'name' (from db1 to db2). The problem is, that 'name' variable in second db is located in another table ...
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1answer
35 views

Will MySQL be effective when selecting a row from a table with billions of records?

Note: this is a hypothetical scenario Lets say that: I'm running MySQL, InnoDB engine, UTF-8 encoding I have a table with 50+ billions of rows The tables primary key is a BIGINT The table also has ...
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1answer
23 views

Mysql will not start

Please help, I really need to recover my databases. service mysql start start: Job failed to start mysqld --verbose 140401 20:16:11 [Warning] Can't create test file ...
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1answer
76 views

What are the disadvantages of PostgreSQL compared to other DBMS? [closed]

I am a student studying PostgreSQL. I want to know the advantages and disadvantages of PostgreSQL in comparison to other DBMS.