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• Store database, good pattern for simultaneous access

  - by dygi

  I am kinda new to database designing so i ask for some advices or some kind of a good pattern. The situation is that, there is one database, few tables and many users. How should i design the database, or / and which types of queries should i use, to make it work, if users can interact with the database simultaneously? I mean, they have access to and can change the same set of data. I was thinking about transactions, but I am not sure, if that is the right / good / the only solution. I will appreciate some google keywords too.

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• How to recalculate primary index?

  - by JohnM2

  I have table in mysql database with autoincrement PRIMARY KEY. On regular basis rows in this table are being deleted an added. So the result is that value of PK of the latest row is growing very fast, but there is not so much rows in this table. What I want to do is to "recalculate" PK in this way, that the first row has PK = 1, second PK = 2 and so on. There are no external dependencies on PK of this table so it would be "safe". Is there anyway it can be done using only mysql queries/tools? Or I have to do it from my code?

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• Using multiple databases within one application (ASP.NET MVC, LINQ to SQL)

  - by Alex

  I have a web application made for several groups of people not connected with each other. Instead of using one database for all of them, I'm thinking about making separate databases. This will improve the speed of the queries and make me free from checking to what group the user belongs. But since I'm working with LINQ to SQL, my classes are explicitly connected with the databases, so I will have to make separate DataContexts for all of the databases. So how can I solve this problem? Or should I just not bother and use one database only?

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• FlockDB - What is it? And best cases for it uses.

  - by Guru

  Just came across FlockDB graph database. Details at github /flockDB. Twitter claims it uses FlockDB for the following: Twitter runs FlockDB on a large cluster of machines. we use it to store social graphs (who follows whom, who blocks whom) and secondary indices at twitter. At first glance, setup and trying it doesn't look straight forward. Have anyone already used it / setup this? If so, please answer the following general queries. What kind of applications is it better suited for? (Twitter claims it is simple and very rough, it remains to see what it meant though) How is FlockDB better than other graph db / noSQL db. Have you setup FlockDB, used it for a application? Early advices any? Note: I am evaluating the FlockDB and other graph databases mainly for learning them. Perhaps, I will build an application for that.

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• Symfony 1.4: Deleting a sfGuardUser

  - by Tom

  Hi, I'm having some trouble with the following... I have a sfGuardUser table set up normally, and it has a one-to-one relationship with a Profile table, which contains some additional user info. When a user wants to delete themselves from the site, I'd like to retain their info in the Profile table for various purposes BUT delete the sfGuardUser in order to keep that table cleaner/shorter (not just set it to inactive). I was under the impression that I could set the FK in the Profile table to NULL and then delete the sfGuardUser, but it seems the FK-constraint fails. Indeed, it seems I can't delete either and the queries fail: If I try to delete the sfGuardUser, the Profile table will have an invalid FK If I try to delete a Profile, the sfGuardUser will have an invalid FK Other than leaving outdated sfGuardUsers and Profiles in these tables, or having to use a cascaded delete to get rid of both, can anyone tell me if there's any other way around this? Thank you.

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• Getting the most frequent items without counting every item

  - by DeadMonkeyWalkin

  Hi. I was wondering if there was an algorithm for counting "most frequent items" without having to keep a count of each item? For example, let's say I was a search engine and wanted to keep track of the 10 most popular searches. What I don't want to do is keep a counter of every query since there could be too many queries for me to count (and most them will be singletons). Is there a simple algorithm for this? Maybe something that is probabilistic? Thanks!

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• Repetitive SQL: What does it mean?

  - by Lijo

  Hi In a different post I got a reply that tells about Repetitive SQL. Could you please explain what is Repetitive SQL? http://stackoverflow.com/questions/2657459/sql-code-smells I thought to make it a new post as it is a different subject. The reply says that use of "multiple stored procedures that perform the exact same joins but different filters" can be avoided using VIEWs. Could you please give an example that can only be achieved using repetitive queries, if we are using Stored Proecure? [The same can be achieved without repetition when used VIEWS] Thanks Lijo

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• What is a good format for command line output when it is being used for further processing?

  - by Mick

  I have written a console application in Delphi that queries information from several locations. This application will be launched by another process, and the output to STDOUT will be captured by the launching process. The information I am retrieving is to be interpreted by the calling application for reporting purposes. What is the best way to output this data to STDOUT so that it can be easily parsed? JSON? XML? CSV? The data, specifically, is remote workstation information, so it will pull things back like running processes, and details about each process. Does anyone have any experience with this or suggestions?

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• fast on-demand c++ compilation [closed]

  - by Amit Prakash

  I'm looking at the possibility of building a system where when a query hits the server, we turn the query into c++ code, compile it as shared object and the run the code. The time for compilation itself needs to be small for it to be worthwhile. My code can generate the corresponding c++ code but if I have to write it out on disk and then invoke gcc to get a .so file and then run it, it does not seem to be worth it. Are there ways in which I can get a small snippet of code to compile and be ready as a share object fast (can have a significant start up time before the queries arrive). If such a tool has a permissive license thats a further plus. Edit: I have a very restrictive query language that the users can use so the security threat is not relevant. My own code translates the query into c++ code. The answer mentioning clang is perfect.

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• Aggregate Functions in Index with IBMDB2

  - by Erkan

  Is there any way to pre aggregate results of aggregate functionts (f.i. count()) and store it in an index? The background is: i want to speed up count() queries. So that: Select count(users) from TE123 where region = 'A'; would be supported by an index like Region Count(Users) A 548 E 458 I know that MQTs would also help for this problem. However, in this case it is not possible to use MQT, as we use kind of an ORM and we don't want to define Entities on MQTs. I just slightly remember - one DBA told me - that there is such a function planned for DB2 V10.

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• How do you optimize database performance when providing results for autocomplete/iterative search?

  - by Howiecamp

  Note: In this question I'm using the term "autocomplete" (or "iterative search") to refer to returning search-as-you-type results, e.g. like Google Search gives you. Also my question is not specific to web applications vs. fat client apps. How are SQL SELECT queries normally constructed to provide decent performance for this type of query, especially over arbitrarily large data sets? In the case where the search will only query based on the first n characters (easiest case) am I still issuing a new SELECT result FROM sometable WHERE entry LIKE... on each keypress. Even with various forms of caching this seems like it might result in poor performance. In cases where you want your search string to return results with prefix matches, substring matches, etc. it's an even more difficult problem. Looking at a case of searching a list of contacts, you might return results that match FirstName + LastName, LastName + FirstName, or any other substring.

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• Most efficent way to limit rows returns from union query- TSQL

  - by stephen776

  Hey guys...I have a simple stored proc with two queries joined with a union select name as 'result' from product where... union select productNum as 'result' from product where... I want to limit this to the TOP 10 results... if i put TOP 10 in each seperate query I get 20 results total. What is the most efficient way to limit total results to 10? I dont want to do TOP 5 in each because I may end up in a situation where I have something like 7 "names" and 3 "productsNumbers"

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• HOw do I limit array to a certain number??

  - by mathew

  I do have an array which queries database..what I need to do is control this array to a certain number say 10. but I dont want to set LIMIT in mysql query I need to leave that as it is... $result = mysql_query("SELECT * FROM query ORDER BY regtime DESC"); while($row = mysql_fetch_array($result)) { echo "<img src='bullet.gif' align='absmiddle' class='col1ab'><a class='col1ab' href=".$row['web']." >www.".$row['web']."</a><br>"; } How do I limit this array to certain limit??

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• Anyway to find out the current Windows is in lock mode?

  - by David.Chu.ca

  I have a windows application written in VS 2005. The application makes queries against to sql database in a timer cycle every 2 minutes. If there any data changes, the window will be refreshed with new data. If the user leaves the window, the windows will be automatically locked after a while. There is no sense to keep querying data in ever 2 minutes when the windows is locked; therefore I would like to stop the query when lock is on so that the network data trafic will be reduced and also saves the current windows resources such as memory and CPUs. I am not sure if there is any way to find out the current windows is locked? Not sure if there is any Windows APIs for this purpose if no .Net classes available? My project is in .Net 2.0 and all users are in Windows XP.

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• Finding group maxes in SQL join result

  - by Gene

  Two SQL tables. One contestant has many entries: Contestants Entries Id Name Id Contestant_Id Score -- ---- -- ------------- ----- 1 Fred 1 3 100 2 Mary 2 3 22 3 Irving 3 1 888 4 Grizelda 4 4 123 5 1 19 6 3 50 Low score wins. Need to retrieve current best scores of all contestants ordered by score: Best Entries Report Name Entry_Id Score ---- -------- ----- Fred 5 19 Irving 2 22 Grizelda 4 123 I can certainly get this done with many queries. My question is whether there's a way to get the result with one, efficient SQL query. I can almost see how to do it with GROUP BY, but not quite. In case it's relevant, the environment is Rails ActiveRecord and PostgreSQL.

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• Mapping tables from an existing database to an object -- is Hibernate suited?

  - by Bernhard V

  Hello! I've got some tables in an existing database and I want to map them to a Java object. Actually it's one table that contains the main information an some other tables that reference to such a table entry with a foreign key. I don't want to store objects in the database, I only want to read from it. The program should not be allowed to apply any changes to the underlying database. Currently I read from the database with 5 JDBC sql queries and set the results then on an object. I'm now looking for a less code intensive way. Another goal is the learning aspect. Is Hibernate suitable for this task, or is there another ORM framework that better fits my requirement?

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• MySQL inner join different results

  - by Darryl at NetHosted

  I am trying to work out why the following two queries return different results: SELECT DISTINCT i.id, i.date FROM `tblinvoices` i INNER JOIN `tblinvoiceitems` it ON it.userid=i.userid INNER JOIN `tblcustomfieldsvalues` cf ON it.relid=cf.relid WHERE i.`tax` = 0 AND i.`date` BETWEEN '2012-07-01' AND '2012-09-31' and SELECT DISTINCT i.id, i.date FROM `tblinvoices` i WHERE i.`tax` = 0 AND i.`date` BETWEEN '2012-07-01' AND '2012-09-31' Obviously the difference is the inner join here, but I don't understand why the one with the inner join is returning less results than the one without it, I would have thought since I didn't do any cross table references they should return the same results. The final query I am working towards is SELECT DISTINCT i.id, i.date FROM `tblinvoices` i INNER JOIN `tblinvoiceitems` it ON it.userid=i.userid INNER JOIN `tblcustomfieldsvalues` cf ON it.relid=cf.relid WHERE cf.`fieldid` =5 AND cf.`value` REGEXP '[A-Za-z]' AND i.`tax` = 0 AND i.`date` BETWEEN '2012-07-01' AND '2012-09-31' But because of the different results that seem incorrect when I add the inner join (it removes some results that should be valid) it's not working at present, thanks.

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• Accepted date format changed overnight

  - by Eugene Niemand

  Since yesterday I started encountering errors related to date formats in SQL Server 2008. Up until yesterday the following used to work. EXEC MyStoredProc '2010-03-15 00:00:00.000' Since yesterday I started getting out of range errors. After investigating I discovered the date as above is now being interpreted as "the 3rd of the 15th month" which will cause a out of range error. I have been able to fix this using the following format with the "T". EXEC MyStoredProc '2010-03-15T00:00:00.000' By using this format its working fine. Basically all I'm trying to find out is if there is some Hotfix or patch that could have caused this, as all my queries using the first mentioned formats have been working for months. Also this is not a setting that was changed by someone in the company as this is occurring on all SQL 2005/2008 servers

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• Do MySQL Locked Tables affect related Views?

  - by CogitoErgoSum

  So after reading http://stackoverflow.com/questions/1415602/performance-in-pdo-php-mysql-transaction-versus-direct-execution in regards to performance issues I was thinking about I did some research on locking tables in MySQL. On http://dev.mysql.com/doc/refman/5.0/en/table-locking.html Table locking enables many sessions to read from a table at the same time, but if a session wants to write to a table, it must first get exclusive access. During the update, all other sessions that want to access this particular table must wait until the update is done. This part struck me particularly becuase most of our queries will be updates rather than inserts. I was wondering if one created a table called foo on which all updates/inserts were carried out and then a view called foo_view (A copy of foo, or perhaps foo and a linkage of several other tables plus foo) on which all selects occured, would this locking issue still occur? That is, would SELECT quries on foo_view still have to wait for an update to finish on foo?

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• TSQL - compare tables

  - by Rya

  I want to create a stored procedure that compares the results of two queries. If the results of the 2nd table can be found in the first, print 'YES', otherwise, print 'No'. Table 1: SELECT dbo.Roles.RoleName, dbo.UserRoles.RoleID FROM dbo.Roles LEFT OUTER JOIN dbo.UserRoles ON dbo.Roles.RoleID = dbo.UserRoles.RoleID WHERE (dbo.Roles.PortalID = 0) AND (dbo.UserRoles.UserID = 2) Table 2: Declare @RowData as nvarchar(2000) Set @RowData = ( SELECT EditPermissions FROM vw_XMP_DMS_Documents where DocumentID = 2) Select Data from dbo.split(@RowData, ',') For example. Table 1: John Jack James Table 2: John Sally Jane Print 'YES' Is this possible??? Thank you all very much. -R

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• Solr match all aka *:* does not work

  - by Karussell

  Don't know what I did wrong. I have two indices with identical documents in it. The local index was replicated from a master which responds correctly, so the same solrconfig.xml and schema.xml file. But if I query the index on my local machine with *:* I get 0 docs. (other queries on my local machine are working correct) I tried jetty and tomcat for the local index. no success. The *:* behaviour is crucial for me, because some test cases are failing now. Do you have an idea what could be wrong?

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• How to strore Java Date to Mysql datetime...?

  - by user275843

  can any body tell me how can i store Java Date to Mysql datetime...? when i am trying to do so...only date is stored and time remain 00:00:00 in mysql date stores like this... 2009-09-22 00:00:00 i want not only date but also time...like 2009-09-22 08:08:11 please help me.... EDIT---- i am using JPA(Hibernate) with spring mydomain classes uses java.util.Date but i have created tables using handwritten queries... this is my create statement CREATE TABLE ContactUs (id BIGINT auto_increment, userName VARCHAR(30), email VARCHAR(50), subject VARCHAR(100), message VARCHAR(1024), messageType VARCHAR(15), contactUsTime datetime, primary key(id))TYPE=InnoDB;

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• How can I sqldump a huge database?

  - by meder

  SELECT count(*) from table gives me 3296869 rows. The table only contains 4 columns, storing dropped domains. I tried to dump the sql through: $backupFile = $dbname . date("Y-m-d-H-i-s") . '.gz'; $command = "mysqldump --opt -h $dbhost -u $dbuser -p $dbpass $dbname | gzip > $backupFile"; However, this just dumps an empty 20 KB gzipped file. My client is using shared hosting so the server specs and resource usage aren't top of the line. I'm not even given ssh access or access directly to the database so I have to make queries through PHP scripts I upload via FTP ( SFTP isn't an option, again ). Is there some way I can perhaps sequentially download portions of it, or pass an argument to mysqldump that will optimize it? I came across http://jeremy.zawodny.com/blog/archives/000690.html which mentions the -q flag and tried that but it didn't seem to do anything differently.

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• In Java how instance of and type cast(i.e (ClassName)) works on proxy object ?

  - by learner

  Java generates a proxy class for a given interface and provides the instance of the proxy class. But when we type cast the proxy object to our specific Object, how java handles this internally? Is this treated as special scenario? For example I have class 'OriginalClass' and it implements 'OriginalInterface', when I create proxy object by passing 'OriginalInterface' interface java created proxy class 'ProxyClass' using methods in the provided interface and provides object of this class(i.e ProxyClass). If my understanding is correct then can you please answer following queries 1) When I type cast object of ProxyClass to my class OriginalClass this works, but how java is allowing this? Same in case of instace of? 2) As my knowledge java creates a proxy class only with the methods, but what happen when I try to access attributes on this object? 3) Only interface methods are getting implemented in Proxy, but what happens when I try to access a method which not in interface and only mentioned in the class? Thanks, Student

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• MySQL Query still executing after a day..?

  - by Matt Jarvis

  Hi - I'm trying to isolate duplicates in a 500MB database and have tried two ways to do it. One creating a new table and grouping: CREATE TABLE test_table as SELECT * FROM items WHERE 1 GROUP BY title; But it's been running for an hour and in MySQL Admin it says the status is Locked. The other way I tried was to delete duplicates with this: DELETE bad_rows.* from items as bad_rows inner join ( select post_title, MIN(id) as min_id from items group by title having count(*) 1 ) as good_rows on good_rows.post_title = bad_rows.post_title; ..and this has been running for 24hours now, Admin telling me it's Sending data... Do you think either or these queries are actually still running? How can I find out if it's hung? (with Apple OS X 10.5.7)

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