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  • how can i set up a uniqueness constraint in mysql for columns that can be null?

    - by user299689
    I know that in MySQL, UNIQUE constraits don't treat NULL values as equal. So if I have a unique constraint on ColumnX, then two separate rows can have values of NULL for ColumnX and this wouldn't violate the constraint. How can I work around this? I can't just set the value to an arbitrary constant that I can flag, because ColumnX in my case is actually a foreign key to another table. What are my options here? Please note that this table also has an "id" column that is its primary key. Since I'm using Ruby on Rails, it's important to keep this id column as the primary key. Note 2: In reality, my unique key encompasses many columns, and some of them have to be null, because they are foreign keys, and only one of them should be non-null. What I'm actually trying to do is to "simulate" a polymorphic relationship in a way that keep referential integrity in the db, but using the technique outlined in the first part of the question asked here: http://stackoverflow.com/questions/922184/why-can-you-not-have-a-foreign-key-in-a-polymorphic-association

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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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  • Table index design

    - by Swoosh
    I would like to add index(s) to my table. I am looking for general ideas how to add more indexes to a table. Other than the PK clustered. I would like to know what to look for when I am doing this. So, my example: This table (let's call it TASK table) is going to be the biggest table of the whole application. Expecting millions records. IMPORTANT: massive bulk-insert is adding data in this table table has 27 columns: (so far, and counting :D ) int x 9 columns = id-s varchar x 10 columns bit x 2 columns datetime x 5 columns INT COLUMNS all of these are INT ID-s but from tables that are usually smaller than Task table (10-50 records max), example: Status table (with values like "open", "closed") or Priority table (with values like "important", "not so important", "normal") there is also a column like "parent-ID" (self - ID) join: all the "small" tables have PK, the usual way ... clustered STRING COLUMNS there is a (Company) column (string!) that is something like "5 characters long all the time" and every user will be restricted using this one. If in Task there are 15 different "Companies" the logged in user would only see one. So there's always a filter on this one. Might be a good idea to add an index to this column? DATE COLUMNS I think they don't index these ... right? Or can / should be?

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  • Why I can't use template table in dynamic query SQL SERVER 2005

    - by StuffHappens
    Hello! I have the following t-sql code which generates an error Declare @table TABLE ( ID1 int, ID2 int ) INSERT INTO @table values(1, 1); INSERT INTO @table values(2, 2); INSERT INTO @table values(3, 3); DECLARE @field varchar(50); SET @field = 'ID1' DECLARE @query varchar(MAX); SET @query = 'SELECT * FROM @table WHERE ' + @field + ' = 1' EXEC (@query) The error is Must declare the table variable "@table". What's wrong with the query. How to fix it?

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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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  • 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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  • Does Table.InsertOnSubmit create a copy of the original table?

    - by Bryan
    Using InsertOnSubmit seems to have some memory overhead. I have a System.Data.Linq.Table<User> table. When I do table.InsertOnSubmit(user) and then int count = table.Count(), the memory usage of my application increases by roughly the size of the User table, but the count is the number of items before user was inserted. So I'm guess an enumeration after InsertOnSubmit will create a copy of the table. Is that true?

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  • hibernate modeling relationships managed through an intermediate table

    - by shikarishambu
    I have a datamodel that has an intermediate table to manage relationships between entities. For example, tables Person and Organization are related through the Relationship table Party (table) - ID Person (table) - ID (references Party.ID) - name Organization (table) -ID (references Party.ID) -name Relationship (table) -ID (PK) -type (references relationshiptype lookup) -fromID (references Party.ID) -ToID (references Party.ID) -fromDate -ToDate Type+fromID+ToID+fromDate+ToDate is guaranteed to be unique. How do I manage this using hibernate? TIA

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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 to remove empty tables from a MySQL backup file.

    - by user280708
    I have multiple large MySQL backup files all from different DBs and having different schemas. I want to load the backups into our EDW but I don't want to load the empty tables. Right now I'm cutting out the empty tables using AWK on the backup files, but I'm wondering if there's a better way to do this. If anyone is interested, this is my AWK script: EDIT: I noticed today that this script has some problems, please beware if you want to actually try to use it. Your output may be WRONG... I will post my changes as I make them. # File: remove_empty_tables.awk # Copyright (c) Northwestern University, 2010 # http://edw.northwestern.edu /^--$/ { i = 0; line[++i] = $0; getline if ($0 ~ /-- Definition/) { inserts = 0; while ($0 !~ / ALTER TABLE .* ENABLE KEYS /) { # If we already have an insert: if (inserts > 0) print else { # If we found an INSERT statement, the table is NOT empty: if ($0 ~ /^INSERT /) { ++inserts # Dump the lines before the INSERT and then the INSERT: for (j = 1; j <= i; ++j) print line[j] i = 0 print $0 } # Otherwise we may yet find an insert, so save the line: else line[++i] = $0 } getline # go to the next line } line[++i] = $0; getline line[++i] = $0; getline if (inserts > 0) { for (j = 1; j <= i; ++j) print line[j] print $0 } next } else { print "--" } } { print }

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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 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 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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  • 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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  • Creating a mySQL query using PHP form dropdowns - If user ignores dropdown, do not filter by that pa

    - by user303043
    Hello, I am creating a simple MySQL query that will be built from the user selecting options from 2 dropdowns. The issue I am having is that I would like each drop down to default that if they do not actually choose an option, do not filter by that dropdown parameter. So, if they come in, and simply hit submit without choosing from a dropdown they should see everything. If they come in and pick from only one of the dropdowns, the query will basically ignore filtering by the other dropdown. I tried making <OPTION VALUE='any'>Choose but my query didn't know what to do with the 'any' and just shows no results. Here is my code. Thank you very much for whatever help you can provide. FORM <form method="POST" action="<?php echo $_SERVER['REQUEST_URI']; ?>"> <select name="GameType"> <OPTION VALUE='any'>Choose Game Type <option value="Game1">Option 1</option> <option value="Game2">Option 2</option> <option value="Game3">Option 3</option> </select> <select name="Instructor"> <OPTION VALUE='any'>Choose Instructor <option VALUE="InstructorA">Instructor A</option> <option value="InstructorB">Instructor B</option> <option value="InstructorC">Instructor C</option> </select> <input type='submit' value='Search Videos'> </form> MYSQL <?PHP connection stuff $db_handle = mysql_connect($server, $user_name, $password); $db_found = mysql_select_db($database, $db_handle); if ($db_found) { $SQL = "SELECT * FROM Videos WHERE GameType=\"{$_POST['GameType']}\" AND Instructor=\"{$_POST['Instructor']}\""; $result = mysql_query($SQL); while ($db_field = mysql_fetch_assoc($result)) { echo $db_field['ShortDescription'] . ", "; echo $db_field['LongDescription'] . ", "; echo $db_field['GameType'] . ", "; echo $db_field['NumberOfPlayers'] . ", "; echo $db_field['Instructor'] . ", "; echo $db_field['Stakes'] . ", "; echo $db_field['UserPermissionLevel'] . ", "; echo $db_field['DateCreated'] . "<BR>"; } mysql_close($db_handle); } else { print "Database NOT Found "; mysql_close($db_handle); } ?>

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