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• Instrumenting Database Access

  - by Whisk

  Jeff mentioned in one of the podcasts that one of the things he always does is put in instrumentation for database calls, so that he can tell what queries are causing slowness etc. This is something I've measured in the past using SQL Profiler, but I'm interested in what strategies other people have used to include this as part of the application. Is it simply a case of including a timer across each database call and logging the result, or is there a 'neater' way of doing it? Maybe there's a framework that does this for you already, or is there a flag I could enable in e.g. Linq-to-SQL that would provide similar functionality. I mainly use c# but would also be interested in seeing methods from different languages, and I'd be more interested in a 'code' way of doing this over a db platform method like SQL Profiler.

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• Help with grasping (INNER?) JOIN

  - by Greenie

  I'm having trouble building a query. I can do what I want in 3 different queries. SELECT id FROM table1 WHERE url LIKE '%/$downloadfile' put that in $url_id SELECT item_id FROM table2 WHERE rel_id = '$url_id'" put that in $item_id SELECT rel_id FROM table2 WHERE rel_id = '$item_id' AND field_id = '42'" put that in $user_id But from reading examples on joins and inner joins I think there's a more elegant way. I cant wrap my brain around writing a better query (but would like to) I can describe how it should go: table1 fields: id, url table2 fields item_id, rel_id, field_id I know the last part of table1.url (LIKE '%/$filename') with that I select table1.id. table1.id is equal to one entry in table2.rel_id. So get that and select the table2.item_id. In table2 there is another entry which has the same table2.item_id and it will have a table2.field_id = '42' And finally the value I need is the table2.rel_id where the table2.field_id was 42. I will fetch that value and put it in $user_id Can this be done with one query using joins/inner joins?

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• Avoiding dog-piling or thundering herd in a memcached expiration scenario

  - by Quintin Par

  I have the result of a query that is very expensive. It is the join of several tables and a map reduce job. This is cached in memcached for 15 minutes. Once the cache expires the queries are obviously run and the cache warmed again. But at the point of expiration the thundering herd problem issue can happen. One way to fix this problem, that I do right now is to run a scheduled task that kicks in the 14th minute. But somehow this looks very sub optimal to me. Another approach I like is nginx’s proxy_cache_use_stale updating; mechanism. The webserver/machine continues to deliver stale cache while a thread kicks in the moment expiration happens and updates the cache. Has someone applied this to memcached scenario though I understand this is a client side strategy? If it benefits, I use Django.

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• How to find duplicate values in SQL Server

  - by hgulyan

  Hi, I'm using SQL Server 2008. I have a table Customers customer_number int field1 varchar field2 varchar field3 varchar field4 varchar ... and a lot more columns, that doesn't matter for my queries. Column *customer_number* is pk. I'm trying to find duplicate values and some differences between them. Please, help me to find all rows that have same 1) field1, field2, field3, field4 2) only 3 columns are equal and one of them isn't (except rows from list 1) 3) only 2 columns equal and two of them aren't (except rows from list 1 and list 2) In the end, I'll have 3 tables with this results and additional groupId, which will be same for a group of similars (For example, for 3 column equals, rows that have 3 same columns equal will be a seperate group) Thank you.

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• Using Rails and Rspec, how do you test that the database is not touched by a method

  - by Will Tomlins

  So I'm writing a test for a method which for performance reasons should achieve what it needs to achieve without using SQL queries. I'm thinking all I need to know is what to stub: describe SomeModel do describe 'a_getter_method' do it 'should not touch the database' do thing = SomeModel.create something_inside_rails.should_not_receive(:a_method_querying_the_database) thing.a_getter_method end end end EDIT: to provide a more specific example: class Publication << ActiveRecord::Base end class Book << Publication end class Magazine << Publication end class Student << ActiveRecord::Base has_many :publications def publications_of_type(type) #this is the method I am trying to test. #The test should show that when I do the following, the database is queried. self.publications.find_all_by_type(type) end end describe Student do describe "publications_of_type" do it 'should not touch the database' do Student.create() student = Student.first(:include => :publications) #the publications relationship is already loaded, so no need to touch the DB lambda { student.publications_of_type(:magazine) }.should_not touch_the_database end end end So the test should fail in this example, because the rails 'find_all_by' method relies on SQL.

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• Building html tables from query data... faster?

  - by Andrew Heath

  With my limited experience/knowledge I am using the following structure to generate HTML tables on the fly from MySQL queries: $c = 0; $t = count($results); $table = '<table>'; while ($c < $t) { $table .= "<tr><td>$results[0]</td><td>$results[1]</td> (etc etc) </tr>"; ++$c; } $table .= '</table>'; this works, obviously. But for tables with 300+ rows there is a noticeable delay in pageload while the script builds the table. Currently the maximum results list is only about 1,100 rows, and the wait isn't long, but there's clearly a wait. Are there other methods for outputting an HTML table that are faster than my WHILE loop? (PHP only please...)

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• java jdbc connection to mysql problem

  - by fatnjazzy

  Hi, I am trying to connect to mysql from java web application in eclipse. Connection con = null; try { //DriverManager.registerDriver(new com.mysql.jdbc.Driver()); Class.forName("com.mysql.jdbc.Driver"); con = DriverManager.getConnection("jdbc:mysql://localhost/db_name","root" ,""); if(!con.isClosed()) System.out.println("Successfully connected to " + "MySQL server using TCP/IP..."); } catch(Exception e) { System.err.println("Exception: " + e.getMessage()); } finally { try { if(con != null) con.close(); } catch(SQLException e) { System.out.println(e.toString()); } } I am always getting the Exception: com.mysql.jdbc.Driver I have downloaded this jar http://forums.mysql.com/read.php?39,218287,220327 import it to the "java build path/lib" the mysql version is 5.1.3 under. running: mysql 5.1.3 (db is up and running queries form PHP) windows XP java jee Thanks

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• how do i use MySql ENUM type? (and is it right for a news feed)

  - by Haroldo

  I'm creating a table called news_feed, this will log all the actions a user performs. Lets say I want to store user1234 deleted article412 at midday I then need a table like so timestamp | user_id | subject_type | subject_id | method . there would be 5 potential methods to log, methods = add/edit/delete/update/report and lets say 2 possible subject_type subjects = article/comment I know i could make my own key where 0=add, 1=delete etc etc but this would make my queries cumbersome to use/write as i'd need to keep consulting the key. Is there a MySql type which can read lots of identially values quickly? is this ENUM? how do i use it?!!

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• Favoriting system on Appengine

  - by Mateusz Cieslak

  Hi, I have the following model structure class Authors(db.Model) : nickname = db.StringProperty(required=True) fullname = db.StringProperty(required=True) class Articles(db.Model) : title = db.StringProperty(required=True) body = db.StringProperty(required=True) author = db.ReferenceProperty(Authors, required=True) class Favorites(db.Model) : who = db.ReferenceProperty(Authors, required=True) what = db.ReferenceProperty(Articles, required=True) I'd like to display 10 last articles according to this pattern: article.title, article.body, article.author(nickname), info if this article has been already favorited by the signed in user. I have added a function which I use to get the authors of these articles using only one query (it is described here) But I don't know what to do with the favorites (I'd like to know which of the displayed articles have been favorited by me using less than 10 queries (I want to display 10 articles)). Is it possible?

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• Why would a TableAdapter populate a DataSet with "1/1/2000" for an entire timestamp column?

  - by Rob

  I have a TableAdapter filling a DataSet, and for some reason every select query populates my timestamp column with the value 1/1/2000 for every selected row. I first verified that original values are intact on the DB side; for the most part, they are, although it seems a few rows lost their original timestamp because of update queries performed programmatically before the issue was discovered. The DataColumn type is DateType, while the database (Postgres) column type is timestamp. Up until recently, this was all playing very nicely. I noticed the issue in a bound DataGridView control, and verified that this is not related to data binding by utilizing the 'Preview Data' option in the VS DataSet Editor. Usually when I notice unexpected values popping up in my application it's related to a mis-configured property, type conflict, or another silly mistake I've made. So after checking properties and types, and even recreating the TableAdapter from scratch, to say I'm a little baffled is an understatement. Does anyone have any ideas of what I could do to fix the issue and/or diagnose the cause?

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• Compare range of ip addresses with start and end ip address in MySQL

  - by Maarten

  I have a MySQL table where I store IP ranges. It is setup in the way that I have the start address stored as a long, and the end address (and an id and some other data). Now I have users adding ranges by inputting a start and end ip address, and I would like to check if the new range is not already (partially) in the database. I know I can do a between query, but that doesn't seem to work with 2 different columns, and I also cannot figure out how to pass a range to compare it. Doing it in a loop in PHP is a possibility, but would with a range of e.g. 132.0.0.0-199.0.0.0 be quite a big amount of queries..

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• Complicated conditional SQL query

  - by DevAno1

  I'm not even sure if it's possible but I need it for my Access database. So I have following db structure : Now I need to perform a query that takes category_id from my product and do the magic : - let's say product belongs to console (category_id is in table Console) - from console_types take type_id, where category_id == category_id - but if product belongs to console_game (category_id is in table console_game) - from console_game take game_cat_id, where category_id == category_id I'm not sure if mysql is capable of such thing. If not I'm really f&%ranked up. Maybe there is a way to split this into 2,3 separate queries ?

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• pipelined function

  - by user289429

  Can someone provide an example of how to use parallel table function in oracle pl/sql. We need to run massive queries for 15 years and combine the result. SELECT * FROM Table(TableFunction(cursor(SELECT * FROM year_table))) ...is what we want effectively. The innermost select will give all the years, and the table function will take each year and run massive query and returns a collection. The problem we have is that all years are being fed to one table function itself, we would rather prefer the table function being called in parallel for each of the year. We tried all sort of partitioning by hash and range and it didn't help. Also, can we drop the keyword PIPELINED from the function declaration? because we are not performing any transformation and just need the aggregate of the resultset.

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• Duplicate an AppEngine Query object to create variations of a filter without affecting the base quer

  - by Steve Mayne

  In my AppEngine project I have a need to use a certain filter as a base then apply various different extra filters to the end, retrieving the different result sets separately. e.g.: base_query = MyModel.all().filter('mainfilter', 123) Then I need to use the results of various sub queries separately: subquery1 = basequery.filter('subfilter1', 'xyz') #Do something with subquery1 results here subquery2 = basequery.filter('subfilter2', 'abc') #Do something with subquery2 results here Unfortunately 'filter()' affects the state of the basequery Query instance, rather than just returning a modified version. Is there any way to duplicate the Query object and use it as a base? Is there perhaps a standard Python way of duping an object that could be used? The extra filters are actually applied by the results of different forms dynamically within a wizard, and they use the 'running total' of the query in their branch to assess whether to ask further questions. Obviously I could pass around a rudimentary stack of filter criteria, but I'd rather use the Query itself if possible, as it adds simplicity and elegance to the solution.

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• OOP App Architecture: Which layer does a lazy loader sit in?

  - by JW

  I am planning the implemention an Inheritance Mapper pattern for an application component http://martinfowler.com/eaaCatalog/inheritanceMappers.html One feature it needs to have is for a domain object to reference a large list of aggreageted items (10,000 other domain objects) So I need some kind of lazy loading collection to be passed out of the aggregate root domain object to other domain objects. To keep my (php) model scripts organised i am storing them in two folders: MyComponent\ controllers\ models\ domain\ <- domain objects, DDD repository, DDD factory daccess\ <- PoEAA data mappers, SQL queries etc views\ But now I am racking my brains wondering where my lazy loading collection sits. Any suggestions / justifications for putting it in one place over another another? DDD = Domain Driven Design Patterns, Eric Evans - book PoEAA = Patterns of Application Architecture Patterns, Martin Fowler - book

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• Help Forming An SQL Query That Selects The Max Difference Of Two Fields

  - by Frank

  I'm trying to select a record with the most effective votes. Each record has an id, the number of upvotes (int) and the number of downvotes (int) in a MySQL database. I know basic update, select, insert queries but I'm unsure of how to form a query that looks something like: SELECT * FROM topics WHERE MAX(topic.upvotes - topic.downvotes). Please excuse my made up SQL. The tutorials on SQL I find on the internet cover very basic stuff. Does anyone recommend a good book on this subject?

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• C# mysqlreader on same connection error

  - by dominiquel

  Hi, I must find a way to do this in C#, if possible... I must loop on my folder list (mysql table), and for each folder I instanciate I must do another query, but when I do this it says : "There is already an open DataReader associated with this Connection" and I am inside a mysqlreader loop already. Note that I have oversimplified the code just to show you, the fact is that I must do queries inside a mysqlreader loop, and it looks to be impossible as they are on the same connection? MySqlConnection cnx = new MySqlConnection(connexionString); cnx.Open(); MySqlCommand command= new MySqlCommand("SELECT * FROM folder WHERE folder_id = " + id, cnx); MySqlDataReader reader= commande.ExecuteReader(); while (reader.Read()) { this.folderList[this.folderList.Length] = new CFolder(reader.GetInt32"folder_id"), cnx); } reader.Close(); cnx.Close();

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• Mysql - multiple values and between

  - by realshadow

  Hey, I need to select 10 products and display them. Each product has 3 different prices. The select to get the prices looks like this: SELECT * FROM products_loans WHERE CODE IN('10X15/12', '10X15/Q10-10', '10X15/Q20-10') AND 550 BETWEEN PRICE_FROM AND PRICE_TO; Where 550 is the base price. Now this select returns 3 rows, but I want to modify it so it will return 30 results. I dont like the idea to execute 10 queries at once. I know I can easily achieve that with "OR", but I would like to ask if there is some other more elegant way to this. The select "should" look like this: SELECT * FROM products_loans WHERE KOD IN('10X15/12', '10X15/Q10-10', '10X15/Q20-10') AND (550, 325, 780) BETWEEN CENA_OD AND CENA_DO; Note that there is no "price" column or anything in the table which I could use to do a JOIN and I cant modify the table.

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• two where conditions in a mysql query

  - by Kaartz

  I have a table like below |date|dom|guid|pid|errors|QA|comm| |2010-03-22|xxxx.com|jsd3j234j|ab|Yes|xxxxxx|bad| |2010-03-22|xxxx.com|jsd3j234j|ab|No|xxxxxx|| |2010-03-22|xxxx.com|jsd3j234j|if|Yes|xxxxxx|bad| |2010-03-22|xxxx.com|jsd3j234j|if|No|xxxxxx|| |2010-03-22|xxxx.com|jsd3j234j|he|Yes|xxxxxx|bad| |2010-03-22|xxxx.com|jsd3j234j|he|No|xxxxxx|| I want to retrieve the total count of "dom" referred to each "QA" and also I need the count of "errors" detected by the "QA" SELECT date, count(dom), QA FROM reports WHERE date="2010-03-22" GROUP BY QA |2010-03-22|2|ab| |2010-03-22|2|if| |2010-03-22|2|he| SELECT date, count(dom), count(errors), QA FROM reports WHERE errors="Yes" GROUP BY QA |2010-03-22|1|ab| |2010-03-22|1|if| |2010-03-22|1|he| I want to combine the above two queries, is it possible. If I use the below query, I am not getting the desired result. SELECT date, count(dom), QA, count(errors) FROM reports WHERE date="2010-03-22" AND errors="Yes" GROUP BY QA I want the below output |2010-03-22|2|ab|1| |2010-03-22|2|if|1| |2010-03-22|2|he|1| Please help me.

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• HBase as web app backend

  - by NathanD

  Can anyone advise if it is a good idea to have HBase as primary data source for web-based application? My primary concern is HBase's response time to queries. Is it possible to have sub-second response? edit: more details about the app itself. Amount of data: ~500GB of text data, expect to reach 1TB soon Number of concurrent users using the app: up to 50 The app will be used to present reports about data stored in HBase, like how many times keyword "X" occured in last 24h. For ~80% of requests from that app I will know the exact key, 20% will be scans (I'm looking into HBase schema design related topics to make it run fast)

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• Parsing HTML with XPath and PHP

  - by Peter

  Is there a way (using XPath and PHP) to do the following (WITHOUT external XSLT files)? Remove all tables and their contents Remove everything after the first h1 tag Keep only paragraphs (INCLUDING their inner HTML (links, lists, etc)) I received an XSLT answer here, but I'm looking for XPATH queries that don't require external files. Currently, I've got the HTML in question loaded into a SimpleXmlElement via: $doc = @DOMDocument::loadHTML($xml); $data = simplexml_import_dom($doc); Now I need help with: $data = $data->xpath('??????'); Been working with this one for several days to no avail. I really appreciate the help. Edit: I don't particularly care what's inside the paragraphs, as I can use strip_tags to eliminate what I don't want. All I need to do is to isolate the paragraphs from the rest of the source. I suppose a more specific, accurate requirement would be this: Return only paragraphs (and their html contents) that aren't contained in tables, and only before the first h1 tag

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• Adding a MongoDB collection to Netbeans

  - by Saif Bechan

  In Netbeans I have an option to add my mysql databases to netbeans. This way I can easily browse and so small queries. Now I am working on a MongoDB project, and I want to know if it is possible to use the same functionality. I see that on the website of mongo there is a list of drivers, and I see that you can add drivers in netbeans. I do not know if the same thing, or if this can be used. I have tried google, but no luck. Anyone have an idea?

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• count(*) is it really expensive ?

  - by Anil Namde

  I have a page where i have 4 tabs displaying 4 different reports based of different tables. Now i get row count of each tabled using select count() from table query and display number of rows available in each table on the tabs. Now with each page post back 5 count() queries are executed (4 to get counts and 1 for pagination) and 1 query for getting report. Now my question is should is count(*) query really expensive that i should keep the row counts (at least which are displayed on tab) in view state of page instead of queering each time? How much expensive it is ?

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• Regex for finding valid sphinx fields

  - by mlissner

  I'm trying to validate that the fields given to sphinx are valid, but I'm having difficulty. Imagine that valid fields are cat, mouse, dog, puppy. Valid searches would then be: @cat search terms @(cat) search terms @(cat, dog) search term @cat searchterm1 @dog searchterm2 @(cat, dog) searchterm1 @mouse searchterm2 So, I want to use a regular expression to find terms such as cat, dog, mouse in the above examples, and check them against a list of valid terms. Thus, a query such as: @(goat) Would produce an error because goat is not a valid term. I've gotten so that I can find simple queries such as @cat with this regex: (?:@)([^( ]*) But I can't figure out how to find the rest. I'm using python & django, for what that's worth.

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• What to read as a good intro and quickstart to aspect-oriented programming and metaprogramming?

  - by Ivan

  As I've found myself repeating myself a lot, writing very similar queries and classes for different entities (despite of doing strong object and relational normalisation), etc, I've came to an Idea that I could and should automate the most of this and write an engine which will compile simple declarative models I specify into all the code limiting my job to describe the task and and finally just customise the result as needed. As far as I know this is about metaprogramming and aspect-oriented programming. How do I get acquainted with modern tools available quickly so that I don't invent one more bicycle developing my own?

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