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  • Are Conditional subquery

    - by Tobias Schulte
    I have a table foo and a table bar, where each foo might have a bar (and a bar might belong to multiple foos). Now I need to select all foos with a bar. My sql looks like this SELECT * FROM foo f WHERE [...] AND ($param IS NULL OR (SELECT ((COUNT(*))>0) FROM bar b WHERE f.bar = b.id)) with $param being replaced at runtime. The question is: Will the subquery be executed even if param is null, or will the dbms optimize the subquery out?

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  • MySQL - Calculate the net time difference between two date-times while excluding breaks?

    - by John M
    In a MySQL query I am using the timediff/time_to_sec functions to calculate the total minutes between two date-times. For example: 2010-03-23 10:00:00 - 2010-03-23 08:00:00 = 120 minutes What I would like to do is exclude any breaks that occur during the selected time range. For example: 2010-03-23 10:00:00 - 2010-03-23 08:00:00 - (break 08:55:00 to 09:10:00) = 105 minutes Is there a good method to do this without resorting to a long list of nested IF statements?

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  • INSERT DELAYED on locked tables blocks PHP processes to continue

    - by sw0x2A
    Our webservers write some tracking information into a MySQL database (using INSERT DELAYED into MyISAM table). When a huge SELECT query is executed on this table or when it is locked for another reason, the webserver processes (with INSERT DELAYED) are waiting for the database and in some cases the MaxServer limit is reached in Apaches, so they will stop serving requests. We use INSERT DELAYED because The DELAYED option for the INSERT statement is a MySQL extension to standard SQL that is very useful if you have clients that cannot or need not wait for the INSERT to complete. This is a common situation when you use MySQL for logging and you also periodically run SELECT and UPDATE statements that take a long time to complete. Quote from MySQL documentation. I am wondering why the Apache processes are waiting for the INSERT DELAYED to finish. And what can I do to just send the data and forget about it. (Since this is logging data, I do not care if we lose some entries.) Even when the table is locked the PHP script should just go on and should not wait for an answer of MySQL. (We do not want to setup Master-slave for this table but we are thinking about move this data to some NoSQL database. But for now I would like to know why INSERT DELAYED is not working as expected.)

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  • mysqldump is not dumping my data

    - by oompahloompah
    I am running mysqldump on Ubuntu Linux (10.0.4 LTS) my mySQL version info is: mysql Ver 14.14 Distrib 5.1.41, for debian-linux-gnu (i486) using readline 6.1 I used the following command: mysql -u username -p dbname dbname_backup.sql However when I opened the generated .sql file, I saw that most of the tables had only the schema dumped and in the few cases where the actual data was dumped, only 1 or two records were dumped (there are ATLEAST several tens of records in each table). Does anyone know what maybe going on?

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  • Does the number of rows in mysql table matter?

    - by 1s2a3n4j5e6e7v
    I'm coming up with a web app which will want me to store more than 80 Lakh (8 million) rows. Will it be fine to handle those many number of rows with MySQL without having any performance degradation? Assume my RAM to be 4 GB and Infinity GB Harddisk space. Also, the main fields have been indexed.

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  • Scaling a LAMP website hosted on EC2

    - by Gublooo
    Hello, I'm very new to all this - I've recently managed to launch my website on EC2. As next step, I want to learn how to scale the website. I have a general idea but wanted some input from the experts about how to go about it. My website is based on LAMP but also has Red5 server which allows users to record messages and also used for playing them back. Currently this is the architecture I'm planning to setup for initial scaling. Deploy four small EC2 instances for the following purposes: Instance-1: On this instance I will run the MySql database Instance-2: On this instance I will run the red5 server Instance-3 & Instance-4 These 2 instances will be used to deploy the website and will have Apache running on them. They will communicate with the mysql server on Instance-1 and red5 server on Instance-2 using the internal IP address. As an when required, I will launch another instance of the same EBS - I will have EBS of say 50 GIG where all the mysql data will be stored. Also red5 will use this EBS to store the video messages Load-Balancer - Use the load balancer provided by Amazon to load balance Instance-3 and Instance-4 This is what I have in mind. I could be way off so please bear with me. Also I have not taken into account the case of scaling MySql server as I currently have no idea about how that will be done and whether or not it is necessary initially. I am aware that Amazon provides auto scaling and mysql scaling as well but I dont want to get into that right now. Your feedback is appreciated Thanks

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  • MysqlTunner and query_cache_size dilemma

    - by wbad
    On a busy mysql server MySQLTuner 1.2.0 always recommends to add query_cache_size no matter how I increase the value (I tried up to 512MB). On the other hand it warns that : Increasing the query_cache size over 128M may reduce performance Here are the last results: >> MySQLTuner 1.2.0 - Major Hayden <[email protected]> >> Bug reports, feature requests, and downloads at http://mysqltuner.com/ >> Run with '--help' for additional options and output filtering -------- General Statistics -------------------------------------------------- [--] Skipped version check for MySQLTuner script [OK] Currently running supported MySQL version 5.5.25-1~dotdeb.0-log [OK] Operating on 64-bit architecture -------- Storage Engine Statistics ------------------------------------------- [--] Status: +Archive -BDB -Federated +InnoDB -ISAM -NDBCluster [--] Data in InnoDB tables: 6G (Tables: 195) [--] Data in PERFORMANCE_SCHEMA tables: 0B (Tables: 17) [!!] Total fragmented tables: 51 -------- Security Recommendations ------------------------------------------- [OK] All database users have passwords assigned -------- Performance Metrics ------------------------------------------------- [--] Up for: 1d 19h 17m 8s (254M q [1K qps], 5M conn, TX: 139B, RX: 32B) [--] Reads / Writes: 89% / 11% [--] Total buffers: 24.2G global + 92.2M per thread (1200 max threads) [!!] Maximum possible memory usage: 132.2G (139% of installed RAM) [OK] Slow queries: 0% (2K/254M) [OK] Highest usage of available connections: 32% (391/1200) [OK] Key buffer size / total MyISAM indexes: 128.0M/92.0K [OK] Key buffer hit rate: 100.0% (8B cached / 0 reads) [OK] Query cache efficiency: 79.9% (181M cached / 226M selects) [!!] Query cache prunes per day: 1033203 [OK] Sorts requiring temporary tables: 0% (341 temp sorts / 4M sorts) [OK] Temporary tables created on disk: 14% (760K on disk / 5M total) [OK] Thread cache hit rate: 99% (676 created / 5M connections) [OK] Table cache hit rate: 22% (1K open / 8K opened) [OK] Open file limit used: 0% (49/13K) [OK] Table locks acquired immediately: 99% (64M immediate / 64M locks) [OK] InnoDB data size / buffer pool: 6.1G/19.5G -------- Recommendations ----------------------------------------------------- General recommendations: Run OPTIMIZE TABLE to defragment tables for better performance Reduce your overall MySQL memory footprint for system stability Increasing the query_cache size over 128M may reduce performance Variables to adjust: *** MySQL's maximum memory usage is dangerously high *** *** Add RAM before increasing MySQL buffer variables *** query_cache_size (> 192M) [see warning above] The server has 76GB ram and dual E5-2650. The load is usually below 2. I appreciate your hints to interpret the recommendation and optimize the database configs.

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  • sql query need a help.

    - by benjamin button
    If i have a table with two fields.customer id and order. let's say i have in total order ID 1,2,3,4 all the customer can have all the four orders.like below 1234 1 1234 2 1234 3 1234 4 3245 3 3245 4 5436 2 5436 4 you can see above that 3245 customer doesnt have order id 1 and 2. how could i print in the query output like 3245 1 3245 2 5436 1 5436 3 EDIT: i dont order table but i have list of order's like we can hard code it in the query(1,2,3,4) i dont have an orders table.

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  • Sorting mysql array value after string chars swapped from fetched DB data.

    - by Shail Patel
    I want to sort one column fetched from mysql DB, and stored in an array. After fetching I am doing below steps. 1- DB Fetching fields array in row format. ->Field1, Field2, Field3, Field4, Field5 2- From that fields array One columns data [Field3], swapping string keywords. eg. AB013, DB131, RS001 to->013AB, 131DB, 001RS Now I want to sort above value in new string format like-> 001RS, 013AB, 131DB

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  • How can I tell when a MySQL table was last updated?

    - by RaGE
    In the footer of my page, I would like to add something like "last updated the xx/xx/200x"; with this date being the last time a certain mySQL table has been updated. What is the best way to do that ? Is there a function to retrieve the date ? Should I make an access to the database everytime my footer is displayed ?

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  • How to update a table using a select group by in a second one and itself as the data source in MySQL

    - by Jader Dias
    I can do this: SELECT t2.value + sum(t3.value) FROM tableA t2, tableB t3 WHERE t2.somekey = t3.somekey GROUP BY t3.somekey But how to do this? UPDATE tableA t1 SET speed = ( SELECT t2.value + sum(t3.value) FROM tableA t2, tableB t3 WHERE t2.somekey = t3.somekey AND t1.somekey = t3.somekey GROUP BY t3.somekey ) ; MySQL says it's illegal since you can't specify target table t1 for update in FROM clause.

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  • Fill in missing values in a SELECT statement

    - by benjamin button
    If i have a table with two fields.customer id and order. let's say i have in total order ID 1,2,3,4 all the customer can have all the four orders.like below 1234 1 1234 2 1234 3 1234 4 3245 3 3245 4 5436 2 5436 4 you can see above that 3245 customer doesnt have order id 1 and 2. how could i print in the query output like 3245 1 3245 2 5436 1 5436 3 EDIT: i dont have order table but i have list of order's like we can hard code it in the query(1,2,3,4) i dont have an orders table.

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  • How I can Optimize this mySQL transaction within java code?

    - by worldpython
    Dear All, I am new to MySql database. I've large table(ID,...). I select ID frequently with java code and.And that make a heavy load on transaction select from tableName where ID=someID notes: 1.Database could be 100,000 records 2.I can't cache result 3.ID is a primary key 4.I try to optimize time needed to return result from query. Any ideas for optimization ? thanks in advance

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  • How to make phpMyAdmin ask for my username and password

    - by anitha
    I am using rhel 5 and php 5 with mysql 5. My server is already configured and running all applications smoothly. I am accessing mysql as root and supplying my password. However, when I access phpmyadmin through browser, it is not asking for my password. Somebody please tell me how can I set it to prompt for username and password. Since I am not familiar with php and mysql please tell me how to do it in simple way.

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