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  • Does the order of columns matter in a group by clause?

    - by Jeff Meatball Yang
    If I have two columns, one with very high cardinality and one with very low cardinality (unique # of values), does it matter in which order I group by? Here's an example: select dimensionName, dimensionCategory, sum(someFact) from SomeFact f join SomeDim d on f.dimensionKey = d.dimensionKey group by d.dimensionName, -- large number of unique values d.dimensionCategory -- small number of unique values Are there situations where it matters?

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  • Extracting a string between specified characters in python

    - by Seth
    I'm a newbie to regular expressions and I have the following string: sequence = ["{\"First\":\"Belyuen,NT,0801\",\"Second\":\"Belyuen,NT,0801\"}","{\"First\":\"Larrakeyah,NT,0801\",\"Second\":\"Larrakeyah,NT,0801\"}"] I am trying to extract the text Belyuen,NT,0801 and Larrakeyah,NT,0801 in python. I have the following code which is not working: re.search('\:\\"...\\', ''.join(sequence)) I.e. I want to get the string between characters :\ and \.

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  • Migrating from hand-written persistence layer to ORM

    - by Sergey Mikhanov
    Hi community, We are currently evaluating options for migrating from hand-written persistence layer to ORM. We have a bunch of legacy persistent objects (~200), that implement simple interface like this: interface JDBC { public long getId(); public void setId(long id); public void retrieve(); public void setDataSource(DataSource ds); } When retrieve() is called, object populates itself by issuing handwritten SQL queries to the connection provided using the ID it received in the setter (this usually is the only parameter to the query). It manages its statements, result sets, etc itself. Some of the objects have special flavors of retrive() method, like retrieveByName(), in this case a different SQL is issued. Queries could be quite complex, we often join several tables to populate the sets representing relations to other objects, sometimes join queries are issued on-demand in the specific getter (lazy loading). So basically, we have implemented most of the ORM's functionality manually. The reason for that was performance. We have very strong requirements for speed, and back in 2005 (when this code was written) performance tests has shown that none of mainstream ORMs were that fast as hand-written SQL. The problems we are facing now that make us think of ORM are: Most of the paths in this code are well-tested and are stable. However, some rarely-used code is prone to result set and connection leaks that are very hard to detect We are currently squeezing some additional performance by adding caching to our persistence layer and it's a huge pain to maintain the cached objects manually in this setup Support of this code when DB schema changes is a big problem. I am looking for an advice on what could be the best alternative for us. As far as I know, ORMs has advanced in last 5 years, so it might be that now there's one that offers an acceptable performance. As I see this issue, we need to address those points: Find some way to reuse at least some of the written SQL to express mappings Have the possibility to issue native SQL queries without the necessity to manually decompose their results (i.e. avoid manual rs.getInt(42) as they are very sensitive to schema changes) Add a non-intrusive caching layer Keep the performance figures. Is there any ORM framework you could recommend with regards to that?

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  • How to check if Thread finished execution

    - by user295502
    I have following problem: I want to check (C#) if thread has finished execution, i.e. if the thread method returned. What I do now is call Thread.Join(1), but this gives 1 ms delay. Is there any way to simply check if thread finished. Inspecting Thread.ThreadState just seems too cumbersome.

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  • How to navigate to another html page?

    - by newbie
    In my application there's a usual login page sending username and password to the server script, where it needs to be authenticated, and in case of an authentic user, the server should redirect to a page student.html. This is my code var ports = 3000; var portt = 3001; var express = require('express'); var student = require('express')(); var teacher = require('express')(); var server_s = require('http').createServer(student); var server_t = require('http').createServer(teacher); var ios = require('socket.io').listen(server_s); var iot = require('socket.io').listen(server_t); var path = require('path'); server_s.listen(ports); server_t.listen(portt); student.use(express.static(path.join(__dirname, 'public'))); student.get('/', function(req,res){ res.sendfile(__dirname + '/login.html'); }); teacher.use(express.static(path.join(__dirname, 'public'))); teacher.get('/', function(req,res){ res.sendfile(__dirname + '/mytry.html'); }); ios.sockets.on('connection', function(socket){ var username, password; socket.on('check',function(data){ username = data[0]; password = data[1]; //************* Database connection and query ************* var mysql = require('mysql'); var connection = mysql.createConnection({ host : 'localhost', user : 'user', password: '*******', database: 'my_db' }); connection.connect(); var qstring = 'SELECT s_id FROM login_student WHERE username='+username+'AND password='+password; connection.query(qstring, function(err, rows, fields) { if (err) { console.log('ERROR: ' + err); socket.emit('login_failure','DB error'); return; } console.log('The solution is: ', rows[0].solution); if (rows>0) //***** Here i want redirection to another page ****** else socket.emit('login_failure','Invalid Username or password'); }); connection.end(); }); }); iot.sockets.on('connection', function(socket){ ; }); }); Can anyone suggest what should I do?

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  • SQL AND operator not working properly

    - by Chandana De Silva
    I have following two tables LandParcels Table Blockid ParcelNo storPri ======= ======== ======= 52000105 3 State 52000105 4 Private 52000105 5 State Actions Table Blockid ParcelNo ActionTaken ======= ======== =========== 52000105 3 Received 52000105 3 Send to Computer 52000105 4 Received 52000105 5 Received I want to find the records Received but not Send to Computer Here is my query select l.blockid, l.parcelno from landparcels l left join actions ac on l.blockid = ac.blockid and l.parcelno = ac.parcelno where ac.actiontaken = 'Received' and ac.actiontaken <> 'Send to Computer' and ac.blockid = 52000105 The result is Blockid ParcelNo ======= ======== 52000105 3 52000105 4 52000105 5 I want ParcelNo 4 and 5

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  • Enity framework not loading relationship even when using include

    - by dilbert789
    I have this code: Category selectedCategory = (from c in DB.Category.Include("SubCategory") join a in DB.Accessory on c.AccCatUID equals a.Category.AccCatUID where a.AccUID == currentAccessory.AccUID select c).FirstOrDefault(); It works fine, selectedCategory gets populated as expected. BUT selectedCategory has a child table 'SubCategory' which does not get loaded even though there is the include there. It is not loaded until I do this: selectedCategory.SubCategory.Load(); Why do I have to call load explicitly in order to load the child table?

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  • Using Page anchors on Google AppEngine?

    - by codingJoe
    I would like to have AppEngine render an html page that auto scrolls to an html anchor point. I'm not how and where to put the that type of instruction. template_values = { 'foo' : 'foo', 'bar': 'bar', 'anchor' : '#MyPageAnchor' # ?? Something like this... } path = os.path.join(os.path.dirname(__file__), fileName) self.response.out.write(template.render(path, template_values)) Is this possible? How do I accomplish this?

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  • please help me to find out where i am doing mistake in this code? i wnat retieve the value that i am

    - by user309381
    function reload(form) { var val = $('seltab').getValue(); new Ajax.Request('Website.php?cat=' +escape(val), { method:'get', onSuccess: function(transport){ var response = transport.responseText ; $("MyDivDB").innerHTML = transport.responseText ; alert("Success! \n\n" + response); }, onFailure: function(){ alert('Something went wrong...') } }); } </script> </head> title author pages $con = mysql_connect($dbhostname,$dbuserid,$dbpassword); if(!$con) { die ("connection failed".mysql_error()); } $db = mysql_select_db($dbname,$con); if(!$db) { die("Database is not selected".mysql_error()); } $query ="SELECT * FROM books NATURAL JOIN authors" ; $result = mysql_query($query); if(!$query) { die("Database is not query".mysql_error()); } while($row = mysql_fetch_array($result,MYSQL_ASSOC)) { $title = $row["title"]; $author = $row["author"]; $page = $row["pages"]; echo "<tr>"; echo "<td>$title</td>"; echo "<td>$author</td>"; echo "<td>$page</td>"; echo "</tr>"; } print "</table>"; echo "<select id = seltab onchange = 'reload(this.form)'>"; $querysel = "SELECT title_id,author FROM authors NATURAL JOIN books"; $result1 = mysql_query($querysel) ; while($rowID = mysql_fetch_assoc($result1)) { $TitleID = $rowID['title_id']; $author = $rowID['author']; print "<option value = $author>$author\n"; print "</option>"; } print "</select>"; ? Wbsite.php

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  • joining relative urls?

    - by heffaklump
    So i want to join strings with relative urls in Javascript. base url = "http://www.adress.com/more/evenmore" with relative url = "../../adress" = "http://www.adress.com/adress" relative url = "../adress" = "http://www.adress.com/more/adress" What would be the best way? I was thinking of using regexp and checking how many "../" i find, then subtracting that amount from the baseurl and adding them to what is left.

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  • Using linq select to provide a grid datasource, properties are read-only

    - by Kelly
    I am using the return from the following call as the datasource for a grid. public object GetPropertyDataSourceWithCheckBox( ) { return ( from p in LocalProperties join c in GetCities( ) on p.CityID equals c.CityID orderby p.StreetNumber select new { Selected = false, p.PropertyID, p.StreetNumber, p.StreetName, c.CityName } ).ToList( ); } I get a checkbox in the grid, but it is READ-ONLY. [For the record, the grid is DevExpress.] Is there a way around this, short of creating a non-anonymous class?

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  • How to list all duplicated rows which may include NULL columns?

    - by Yousui
    Hi guys, I have a problem of listing duplicated rows that include NULL columns. Lemme show my problem first. USE [tempdb]; GO IF OBJECT_ID(N'dbo.t') IS NOT NULL BEGIN DROP TABLE dbo.t END GO CREATE TABLE dbo.t ( a NVARCHAR(8), b NVARCHAR(8) ); GO INSERT t VALUES ('a', 'b'); INSERT t VALUES ('a', 'b'); INSERT t VALUES ('a', 'b'); INSERT t VALUES ('c', 'd'); INSERT t VALUES ('c', 'd'); INSERT t VALUES ('c', 'd'); INSERT t VALUES ('c', 'd'); INSERT t VALUES ('e', NULL); INSERT t VALUES (NULL, NULL); INSERT t VALUES (NULL, NULL); INSERT t VALUES (NULL, NULL); INSERT t VALUES (NULL, NULL); GO Now I want to show all rows that have other rows duplicated with them, I use the following query. SELECT a, b FROM dbo.t GROUP BY a, b HAVING count(*) > 1 which will give us the result: a b -------- -------- NULL NULL a b c d Now if I want to list all rows that make contribution to duplication, I use this query: WITH duplicate (a, b) AS ( SELECT a, b FROM dbo.t GROUP BY a, b HAVING count(*) > 1 ) SELECT dbo.t.a, dbo.t.b FROM dbo.t INNER JOIN duplicate ON (dbo.t.a = duplicate.a AND dbo.t.b = duplicate.b) Which will give me the result: a b -------- -------- a b a b a b c d c d c d c d As you can see, all rows include NULLs are filtered. The reason I thought is that I use equal sign to test the condition(dbo.t.a = duplicate.a AND dbo.t.b = duplicate.b), and NULLs cannot be compared use equal sign. So, in order to include rows that include NULLs in it in the last result, I have change the aforementioned query to WITH duplicate (a, b) AS ( SELECT a, b FROM dbo.t GROUP BY a, b HAVING count(*) > 1 ) SELECT dbo.t.a, dbo.t.b FROM dbo.t INNER JOIN duplicate ON (dbo.t.a = duplicate.a AND dbo.t.b = duplicate.b) OR (dbo.t.a IS NULL AND duplicate.a IS NULL AND dbo.t.b = duplicate.b) OR (dbo.t.b IS NULL AND duplicate.b IS NULL AND dbo.t.a = duplicate.a) OR (dbo.t.a IS NULL AND duplicate.a IS NULL AND dbo.t.b IS NULL AND duplicate.b IS NULL) And this query will give me the answer as I wanted: a b -------- -------- NULL NULL NULL NULL NULL NULL NULL NULL a b a b a b c d c d c d c d Now my question is, as you can see, this query just include two columns, in order to include NULLs in the last result, you have to use many condition testing statements in the query. As the column number increasing, the condition testing statements you need in your query is increasing astonishingly. How can I solve this problem? Great thanks.

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  • Is it possible to use 'else' in a python list comprehension?

    - by Josh
    Here is the code I was trying to turn into a list comprehension: table = '' for index in xrange(256): if index in ords_to_keep: table += chr(index) else: table += replace_with Is there a way to add the else statement to this comprehension? table = ''.join(chr(index) for index in xrange(15) if index in ords_to_keep) Also, would I be right in concluding that a list comprehension is the most efficient way to do this?

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  • Rails send mail with GMail

    - by Danny McClelland
    Hi Everyone, I am on rails 2.3.5 and have the latest Ruby installed and my application is running well, except, GMail emails. I am trying to setup my gmail imap connection which has worked previously but now doesnt want to know. This is my code: # Be sure to restart your server when you modify this file # Uncomment below to force Rails into production mode when # you don't control web/app server and can't set it the proper way # ENV['RAILS_ENV'] ||= 'production' # Specifies gem version of Rails to use when vendor/rails is not present RAILS_GEM_VERSION = '2.3.5' unless defined? RAILS_GEM_VERSION # Bootstrap the Rails environment, frameworks, and default configuration require File.join(File.dirname(__FILE__), 'boot') Rails::Initializer.run do |config| # Gems config.gem "capistrano-ext", :lib => "capistrano" config.gem "configatron" # Make Time.zone default to the specified zone, and make Active Record store time values # in the database in UTC, and return them converted to the specified local zone. config.time_zone = "London" # The internationalization framework can be changed to have another default locale (standard is :en) or more load paths. # All files from config/locales/*.rb,yml are added automatically. # config.i18n.load_path << Dir[File.join(RAILS_ROOT, 'my', 'locales', '*.{rb,yml}')] #config.i18n.default_locale = :de # Your secret key for verifying cookie session data integrity. # If you change this key, all old sessions will become invalid! # Make sure the secret is at least 30 characters and all random, # no regular words or you'll be exposed to dictionary attacks. config.action_controller.session = { :session_key => '_base_session', :secret => '7389ea9180b15f1495a5e73a69a893311f859ccff1ffd0fa2d7ea25fdf1fa324f280e6ba06e3e5ba612e71298d8fbe7f15fd7da2929c45a9c87fe226d2f77347' } config.active_record.observers = :user_observer end ActiveSupport::CoreExtensions::Date::Conversions::DATE_FORMATS.merge!(:default => '%d/%m/%Y') ActiveSupport::CoreExtensions::Time::Conversions::DATE_FORMATS.merge!(:default => '%d/%m/%Y') require "will_paginate" ActionMailer::Base.delivery_method = :smtp ActionMailer::Base.smtp_settings = { :enable_starttls_auto => true, :address => "smtp.gmail.com", :port => 587, :domain => "XXXXXXXX.XXX", :authentication => :plain, :user_name => "XXXXXXXXXX.XXXXXXXXXX.XXX", :password => "XXXXX" } But the above just results in an SMTP auth error in the production log. I have read varied reports of this not working in Rails 2.2.2 but nothing for 2.3.5, anyone got any ideas? Thanks, Danny

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  • ado sql update table with result of group by query

    - by brett
    I am trying to update records in an .mdb table with the number of records containing the same value The sql below does not work but I think gives an indication of what I am trying to achieve. UPDATE table1 AS A INNER JOIN (SELECT PH_BSP , Count(PH_BSP) AS PHCOUNT FROM table1 GROUP BY PH_BSP) AS B ON A.PH_BSP=B.PH_BSP SET A.PH_SORT = B.PHCOUNT; any ideas?

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  • Multiple conditions on select query

    - by stats101
    I have a select statement and I wish to calculate the cubic volume based on other values within the table. However I want to check that neither pr.Length_mm or pr.Width_mm or pr.Height_mm are NULL prior. I've looked at CASE statements, however it only seems to evaluate one column at a time. SELECT sa.OrderName, sa.OrderType, pr.Volume_UOM ,pr.Length_mm*pr.Width_mm*pr.Height_mm AS Volume_Cubic ,pr.Length_mm*pr.Width_mm AS Volume_Floor ,pr.Length_mm ,pr.Height_mm ,pr.Width_mm FROM CostToServe_MCB.staging.Sale sa LEFT JOIN staging.Product pr ON sa.ID = pr.ID

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  • How would I change this Query builder from Kohana 2.4 to Kohana 3?

    - by Thorpe Obazee
    I have had this website built for a few months and I am just getting on Kohana 3. I'd just like to convert this K2.4 query builder to K3 query builder. return DB::select(array('posts.id', 'posts.created', 'posts.uri', 'posts.price', 'posts.description', 'posts.title', 'image_count' => db::expr('COUNT(images.id)'))) ->from('posts') ->join('images')->on('images.post_id', '=', 'posts.id') ->group_by(array('posts.id')) ->order_by('posts.id', 'DESC') ->limit($limit) ->offset($offset) ->execute();

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  • SQL Count in View as column

    - by alex
    I'm trying to get the result of a COUNT as a column in my view. Please see the below query for a demo of the kind of thing I want (this is just for demo purposes) SELECT ProductID, Name, Description, Price, (SELECT COUNT(*) FROM ord WHERE ord.ProductID = prod.ProductID) AS TotalNumberOfOrders FROM tblProducts prod LEFT JOIN tblOrders ord ON prod.ProductID = ord.ProductID This obviously isn't working... but I was wondering what the correct way of doing this would be?

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  • Why does this MySQL Query hang?

    - by zzapper
    SELECT * FROM tbl_order_head AS o INNER JOIN tbl_orders_log AS c ON o.PAYMENT_TRANSACTION_LOG_ID=c.TRANSACTION_ID WHERE o.VISUAL_ID = '77783'; tbl_order_head 67,000 (30 fields) records, tbl_orders_log 17000 (5 fields) records. I don't know if it would eventually return as I am running it on a live server and fear overloading. I am doing similar queries and much more complex queries successfully.

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  • Convert sql query

    - by nisha
    I have used this query in sql,pls convert this query to use for access database. Table structure is UserID,Username,LogDate,LogTime WITH [TableWithRowId] as (SELECT ROW_NUMBER() OVER(ORDER BY UserId,LogDate,LogTime) RowId, * FROM @YourTable), [OddRows] as (SELECT * FROM [TableWithRowId] WHERE rowid % 2 = 1), [EvenRows] as (SELECT *, RowId-1 As OddRowId FROM [TableWithRowId] WHERE rowid % 2 = 0) SELECT [OddRows].UserId, [OddRows].UserName, [OddRows].LogDate, [OddRows].LogTime, [EvenRows].LogDate, [EvenRows].LogTime FROM [OddRows] LEFT JOIN [EvenRows] ON [OddRows].RowId = [EvenRows].OddRowId

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  • MySQL error problem

    - by comma
    I keep getting the error listed below but it only says line 1 what does this mean and how do I fix it? Here is the error I keep getting? You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '1' at line 1 here is the code. if (isset($_POST['info_submitted'])) { $user_id = '5'; $mysqli = mysqli_connect("localhost", "root", "", "sitename"); $dbc = mysqli_query($mysqli,"SELECT learned_skills.*, users_skills.* FROM learned_skills INNER JOIN users_skills ON learned_skills.id = users_skills.skill_id WHERE user_id='$user_id'"); $skill = $_POST['skill']; $experience = $_POST['experience']; $year = $_POST['year']; if (mysqli_num_rows($dbc) == 0) { $mysqli = mysqli_connect("localhost", "root", "", "sitename"); $query1 = mysqli_query($mysqli,"INSERT INTO learned_skills (skill, experience, year) VALUES ('" . $skill . "', '" . $experience . "', '" . $year . "')"); } if (!mysqli_query($mysqli, $query1)) { print mysqli_error($mysqli); return; } $mysqli = mysqli_connect("localhost", "root", "", "sitename"); $dbc = mysqli_query($mysqli,"SELECT id FROM learned_skills WHERE id='" . $skill . "' AND experience='" . $experience . "' AND year='" . $year . "'"); if (!$dbc) { print mysqli_error($mysqli); } else { while($row = mysqli_fetch_array($dbc)){ $id = $row["id"]; } } $query2 = "INSERT INTO users_skills (skill_id, user_id, date_created) VALUES ('$id', '$user_id', NOW())"; if (!mysqli_query($mysqli, $query2)) { print mysqli_error($mysqli); return; } if ($dbc == TRUE) { $dbc = mysqli_query($mysqli,"UPDATE learned_skills JOIN users_skills ON (users_skills.skill_id = learned_skills.id) SET skill = '$skill', experience = '$experience', year = '$year'"); echo '<p class="changes-saved">Your changes have been saved!</p>'; } if (!$dbc) { print mysqli_error($mysqli); return; } }

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  • Postgresql count+sort performance

    - by invictus
    I have built a small inventory system using postgresql and psycopg2. Everything works great, except, when I want to create aggregated summaries/reports of the content, I get really bad performance due to count()'ing and sorting. The DB schema is as follows: CREATE TABLE hosts ( id SERIAL PRIMARY KEY, name VARCHAR(255) ); CREATE TABLE items ( id SERIAL PRIMARY KEY, description TEXT ); CREATE TABLE host_item ( id SERIAL PRIMARY KEY, host INTEGER REFERENCES hosts(id) ON DELETE CASCADE ON UPDATE CASCADE, item INTEGER REFERENCES items(id) ON DELETE CASCADE ON UPDATE CASCADE ); There are some other fields as well, but those are not relevant. I want to extract 2 different reports: - List of all hosts with the number of items per, ordered from highest to lowest count - List of all items with the number of hosts per, ordered from highest to lowest count I have used 2 queries for the purpose: Items with host count: SELECT i.id, i.description, COUNT(hi.id) AS count FROM items AS i LEFT JOIN host_item AS hi ON (i.id=hi.item) GROUP BY i.id ORDER BY count DESC LIMIT 10; Hosts with item count: SELECT h.id, h.name, COUNT(hi.id) AS count FROM hosts AS h LEFT JOIN host_item AS hi ON (h.id=hi.host) GROUP BY h.id ORDER BY count DESC LIMIT 10; Problem is: the queries runs for 5-6 seconds before returning any data. As this is a web based application, 6 seconds are just not acceptable. The database is heavily populated with approximately 50k hosts, 1000 items and 400 000 host/items relations, and will likely increase significantly when (or perhaps if) the application will be used. After playing around, I found that by removing the "ORDER BY count DESC" part, both queries would execute instantly without any delay whatsoever (less than 20ms to finish the queries). Is there any way I can optimize these queries so that I can get the result sorted without the delay? I was trying different indexes, but seeing as the count is computed it is possible to utilize an index for this. I have read that count()'ing in postgresql is slow, but its the sorting that are causing me problems... My current workaround is to run the queries above as an hourly job, putting the result into a new table with an index on the count column for quick lookup. I use Postgresql 9.2.

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