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• Essential skills of a Data Scientist

  - by harshsinghal

  I would like to know more about the relevant skills in the arsenal of a Data Scientist, and with new technologies coming in every day, how one picks and chooses the essentials. A few ideas germane to this discussion: Knowing SQL and the use of a DB such as MySQL, PostgreSQL was great till the advent of NoSql and non-relational databases. MongoDB, CouchDB etc. are becoming popular to work with web-scale data. Knowing a stats tool like R is enough for analysis, but to create applications one may need to add Java, Python, and such others to the list. Data now comes in the form of text, urls, multi-media to name a few, and there are different paradigms associated with their manipulation. What about cluster computing, parallel computing, the cloud, Amazon EC2, Hadoop ? OLS Regression now has Artificial Neural Networks, Random Forests and other relatively exotic machine learning/data mining algos. for company Thoughts?

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• SQL GROUP BY - also SELECT not-constant columns

  - by Michal Kosek

  can someone please help me with this query? I have 2 tables in my database: log_visitors: -------------------- id | host_id log_access: -------------------- visitor | document | timestamp "log_access.visitor" links to "log_visitors.id" Currently, I'm using this query: SELECT log_visitors.host_id , MIM(log_access.timestamp) AS min_timestamp FROM log_access INNER JOIN log_visitors ON (log_access.visitor = log_visitors.id) GROUP BY log_visitors.host_id; to get "MIN(timestamp)" for each "host_id" in the database. HERE'S MY QUESTION: I also need to get "document" for that access with that timestamp... I can't simply add "log_access.document" into SELECT list, since it's not constant and I am not grouping by document... Any ideas?

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• Django DecimalField returns "None" instead of empty value

  - by Ed

  Is there a way to force django to display nothing instead of "None" for a Decimal Field that's been left blank? In my template, I show a list of all the values for a particular field. Each value is hyperlinked to a page that displays the results of a query filtered on that value. But because there are some entries with null value, my list includes actual DecimalField entries and "None" for all those that are empty. When a user clicks on None, django throws a validation error because you cannot query a DecimalField using a string. I could write if statements checking all instances of decimal fields for Nones and skipping them, but that is far from an elegant solution. Any advice? This is one part of the code, though there are other templates that derive the None value in slightly different manners: {% for item in choices %} <a href={% url app_views.field_choice item %}>{{ item }}</a><br> {% endfor %}

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• ORDER BY giving wrong order

  - by Cody Dull

  I have an SQL statement in my C# program that looks like: SELECT * FROM XXX.dbo.XXX WHERE Source = 'OH' AND partnum = '1231202085' ORDER BY partnum, Packaging, Quantity When running this query in SQL Server Management, the results are ordered as expected. My first 3 results have the same partnum and Packaging with Quantities of 32.0, 50.8, and 51.0. However, when I run the query from my program, the result set with quantity 50.8 is the first to be returned. The datatype of Quantity is decimal(18,9). I've tried cast, it doesn't appear to be a datatype problem. I cant figure out why its getting the middle quantity.

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• hibernate order by association

  - by Gary Kephart

  I'm using Hibernate 3.2, and using criteria to build a query. I'd like to add and "order by" for a many-to-one association, but I don't see how that can be done. The Hibernate query would end up looking like this, I guess: select t1.a, t1.b, t1.c, t2.dd, t2.ee from t1 inner join t2 on t1.a = t2.aa order by t2.dd <-- need to add this I've tried criteria.addOrder("assnName.propertyName") but it doesn't work. I know it can be done for normal properties. Am I missing something?

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• SQL joining 3 tables when 1 table is emty

  - by AdRock

  I am trying to write a query that connects 3 tables. The first table is info about each festival The second table is the number of votes for each festival The third table is reviews for each festival I want to join all 3 tables so i get all the feilds from table1, join table1 with table2 on the festivalid but i also need to count the number of records in table 3 that applys to each festival. The first 2 tables give me a result becuase they both have data in them but table 3 is empty becuase there are no reviews yet so adding that to my query fives me no results SELECT f.*, v.total, v.votes, v.festivalid, r.reviewcount as count FROM festivals f INNER JOIN vote v ON f.festivalid = v.festivalid INNER JOIN (SELECT festivalid, count(*) as reviewcount FROM reviews) GROUP BY festivalid) as r on r.festivalid = v.festivalid

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• How to model a social news feed on Google App Engine

  - by PEZ

  We want to implement a "News feed" where a user can see messages broadcasted by her friends, sorted with newest message first. But the feed should reflect changes in her friends list. (If she adds new friends, messages from those should be included in the feed, and if she removes friends their messages should not be included.) If we use the pubsub-test example and attach a recipient list to each message this means a lot of manipulation of the message recipients lists when users connect and disconnect friends. We first modeled publish-subscribe "fan out" using conventional RDBMS thinking. It seemed to work at first, but then, since the IN operator works the way it does, we quickly realized we couldn't continue on that path. We found Brett Slatkin's presentation from last years Google I/O and we have now watched it a few times but it isn't clear to us how to do it with "dynamic" recipient lists. What we need are some hints on how to "think" when modeling this.

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• dilemma about mysql. using condition to limit load on a dbf

  - by ondrobaco

  hi, I have a table of about 800 000 records. Its basically a log which I query often. I gave condition to query only queries that were entered last month in attempt to reduce the load on a database. My thinking is a) if the database goes only through the first month and then returns entries, its good. b) if the database goes through the whole database + checking the condition against every single record, it's actually worse than no condition. What is your opinion? How would you go about reducing load on a dbf?

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• Database solutions for storing/searching EXIF data

  - by webdestroya

  I have thousands of photos on my site (each with a numeric PhotoID) and I have EXIF data (photos can have different EXIF tags as well). I want to be able to store the data effectively and search it. Some photos have more EXIF data than others, some have the same, so on.. Basically, I want to be able to query say 'Select all photos that have a GPS location' or 'All photos with a specific camera' I can't use MySQL (tried it, it doesn't work). I thought about Cassandra, but I don't think it lets me query on fields. I looked at SimpleDB, but I would rather: not pay for the system, and I want to be able to run more advanced queries on the data. Also, I use PHP and Linux, so it would be awesome if it could interface nicely to PHP. Any ideas?

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• Visual Studio error on valid SQL

  - by Sam

  I'm getting an annoying error in visual studio for SQL that executes fine. SELECT InvoiceLines.LineID, InvoiceLines.InvoiceID, InvoiceLines.Text, InvoiceLines.Rate, InvoiceLines.Count, InvoiceLines.Rate * InvoiceLines.Count AS LineTotal, ((InvoiceLines.Rate * InvoiceLines.Count) * (1 + Invoices.VatRate / 100)) * (1 - CAST(Invoices.Discount AS money) * InvoiceLines.ApplyDiscount / 100) AS LineTotalIncVat, InvoiceLines.ApplyDiscount FROM InvoiceLines LEFT JOIN Invoices ON Invoices.InvoiceID = InvoiceLines.InvoiceID What LineTotalIncVat is trying to do is compute the total for the invoice item while adding the vat and subtracting the discount, and yes, probably better to do this in code (would if I could) The error visual studio gives is: There was an error parsing the query [token line number =1, token line offset =14, token in error = InvoiceLines] Even though it will validate and execute without a problem in the query builder...

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• An INSERT conditioned on COUNT

  - by Anders Feder

  How can I construct a MySQL INSERT query that only executes if the number of rows satisfying some condition already in the table is less than 20, and fails otherwise? That is, if the table has 18 rows satisfying the condition, then the INSERT should proceed. If the table has 23 rows satisfying the condition, then the INSERT should fail. For atomicity, I need to express this in a single query, so two requests can not INSERT at the same time, each in the 'belief' that only 19 rows satisfy the condition. Thank you.

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• SQL Server Multiple Joins Are Taxing The CPU

  - by durilai

  I have a stored procedure on SQL Server 2005. It is pulling from a Table function, and has two joins. When the query is run using a load test it kills the CPU 100% across all 16 cores! I have determined that removing one of the joins makes the query run fine, but both taxes the CPU. Select SKey From dbo.tfnGetLatest(@ID) a left join [STAGING].dbo.RefSrvc b on a.LID = b.ESIID left join [STAGING].dbo.RefSrvc c on a.EID = c.ESIID Any help is appreciated, note the join is happening on the same table in a different database on the same server.

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• how to store description in database?

  - by sribharanidharan

  hai i'm using MSAccess database i want to store the description upto more than 255 character please give me the query for inserting the record?in asp.net with c# coding

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• Rendering a variable with erb.

  - by TZer0

  I've got the following problem: I have rhtml (html minced together with ruby inside <% % and <%= % tags) stored in a database which I want to render. The information is acquired through a query. I need to be able to evaluate the information I get from the database as though as it was normal content inside the .erb-file. What I currently have: <% @mymods.each do |mod| %> <%= render_text(mod["html"])%> <% end %> Where mod["html"] is the variable containing the rhtml-code and @mymods an array of objects from the query. I have currently no idea what function I should use (render_text does, of course, not work). Help is greatly appreciated. /TZer0

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• Cross platform unicode path handling

  - by Matt Joiner

  I'm using boost::filesystem for cross-platform path manipulation, but this breaks down when calls need to be made down into interfaces I don't control that won't accept UTF-8. For example when using the Windows API, I need to convert to UTF-16, and then call the wide-string version of whatever function I was about to call, and then convert any output back to UTF-8. While the wpath, and other w* forms of many of the boost::filesystem functions help keep sanity, are there any suggestions for how best to handle this conversion to wide-string forms where needed, while maintaining consistency in my own code?

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• Using multiple aggregate functions in an algebraic expression in (ANSI) SQL statement

  - by morpheous

  I have the following aggregate functions (AGG FUNCs): foo(), foobar(), fredstats(), barneystats(). I want to know if I can use multiple AGG FUNCs in an algebraic expression. This may seem a strange/simplistic question for seasoned SQL developers - however, the but the reason I ask is that so far, all AGG FUNCs examples I have seen are of the simplistic variety e.g. max(salary) < 100, rather than using the AGG FUNCs in an expression which involves using multiple AGG FUNCs in an expression (like agg_func1() agg_func2()). The information below should help clarify further. Given tables with the following schemas: CREATE TABLE item (id int, length float, weight float); CREATE TABLE item_info (item_id, name varchar(32)); # Is it legal (ANSI) SQL to write queries of this format ? SELECT id, name, foo, foobar, fredstats FROM A, B (SELECT id, foo(123) as foo, foobar('red') as foobar, fredstats('weight') as fredstats FROM item GROUP BY id HAVING [ALGEBRAIC EXPRESSION] ORDER BY id AS A), item_info AS B WHERE item.id = B.id Where: ALGEBRAIC EXPRESSION is the type of expression that can be used in a WHERE clause - for example: ((foo(x) < foobar(y)) AND foobar(y) IN (1,2,3)) OR (fredstats(x) <> 0)) I am using PostgreSQL as the db, but I would prefer to use ANSI SQL wherever possible. Assuming it is legal to include AGG FUNCS in the way I have done above, I'd like to know: Is there a more efficient way to write the above query ? Is there any way I can speed up the query in terms of a judicious choice of indexes on the tables item and item_info ? Is there a performance hit of using AGG FUNCs in an algebraic expression like I am (i.e. an expression involving the output of aggregate functions rather than constants? Can the expression also include 'scaled' AGG FUNC? (for example: 2*foo(123) < -3*foobar(456) ) - will scaling (i.e. multiplying an AGG FUNC by a number have an effect on performance?) How can I write the query above using INNER JOINS instead?

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• How do I select the number of distinct days in a date range?

  - by isme

  I'm trying to use the T-SQL function DATEDIFF to select the number of distinct dates in a time period. The following query: SELECT DATEDIFF(DAY, '2012-01-01 01:23:45', '2012-01-02 01:23:45') selects 1, which is one less than I want. There are two distinct dates in the range: 2012-01-01 and 2012-01-02. It is not correct to add one to the result in the general case. The following query: SELECT DATEDIFF(DAY, '2012-01-01 00:00:00', '2012-01-02 00:00:00') selects 1, which is correct, because there is only one distinct date in the range. I'm sure there is a simple bit of arithmetic that I'm missing to calculate this. Can someone help me?

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• How to combine two sql queries?

  - by plasmuska

  Hi Guys, I have a stock table and I would like to create a report that will show how often were items ordered. "stock" table: item_id | pcs | operation apples | 100 | order oranges | 50 | order apples | -100 | delivery pears | 100 | order oranges | -40 | delivery apples | 50 | order apples | 50 | delivery Basically I need to join these two queries together. A query which prints stock balances: SELECT stock.item_id, Sum(stock.pcs) AS stock_balance FROM stock GROUP BY stock.item_id; A query which prints sales statistics SELECT stock.item_id, Sum(stock.pcs) AS pcs_ordered, Count(stock.item_id) AS number_of_orders FROM stock GROUP BY stock.item_id, stock.operation HAVING stock.operation="order"; I think that some sort of JOIN would do the job but I have no idea how to glue queries together. Desired output: item_id | stock_balance | pcs_ordered | number_of_orders apples | 0 | 150 | 2 oranges | 10 | 50 | 1 pears | 100 | 100 | 1 This is just example. Maybe, I will need to add more conditions because there is more columns. Is there a universal technique of combining multiple queries together?

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• TableAdapter to return ONLY selected columns? (VS2008)

  - by MattSlay

  (VS2008) I'm trying to configure a TableAdapter in a Typed DataSet to return only a certain subset of columns from the main schema of the table on which it is based, but it always returns the entire schema (all columns) with blank values in the columns I have omitted. The TableAdpater has the default Fill and GetData() methods that come from the wizard, which contain every column in the table, which is fine. I then added a new parameterized query method called GetActiveJobsByCustNo(CustNo), and I only included a few columns in the SQL query that I actually want to be in this table view. But, again, it returns all the columns in the master table schema, with empty values for the columns I omitted. The reason I am wanting this, is so I can just get a few columns back to use that table view with AutoGenerateColumns in an ASP.NET GridView. With it giving me back EVERY column i nthe schema, my presentation GridView contains way more columns that I want to show th user. And, I want to avoid have to declare the columns in the GridView.

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• mysql result set joining existing table

  - by Yang

  is there any way to avoid using tmp table? I am using a query with aggregate function (sum) to generate the sum of each product: the result looks like this: product_name | sum(qty) product_1 | 100 product_2 | 200 product_5 | 300 now i want to join the above result to another table called products. so that i will have a summary like this: product_name | sum(qty) product_1 | 100 product_2 | 200 product_3 | 0 product_4 | 0 product_5 | 300 i know 1 way of doing this is the dump the 1st query result to a temp table then join it with products table. is there a better way?

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• Write a sql for searching with multiple conditions

  - by Lu Lu

  Hello everyone, I have a table Student with 2 fields: Name: nvarchar(256) Age: int User will use a WinForm application to input a Name and a Age for searching. If inputted Name is empty, sql will not query Name field. If inputted Age is 0, sql will not query Age field. If Name is Null and inputted Name is empty - record is matched. If Name is Null and inputted Name is not empty - record is not matched. And also similar for Age field. My problem is that how to write a sql like this. P/S: I use SQL Server 2005. Please help me. Thanks.

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• Communicate between content script and options page

  - by Gaurang Tandon

  I have seen many questions already and all are about background page to content script. Summary My extension has an options page, and a content script. The content script handles the storage functionality (chrome.storage manipulation). Whenever, a user changes a setting in the options page, I want to send a message to the content script to store the new data. My code: options.js var data = "abcd"; // let data chrome.tabs.query({ active: true, currentWindow: true }, function (tabs) { chrome.tabs.sendMessage(tabs[0].id, "storeData:" + data, function(response){ console.log(response); // gives undefined :( }); }); content script js chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) { // not working }); My question: Why isn't the approach not working? Is there any other (better) approach for this procedure.

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• Understanding SingleTableEntityPersister n QueryLoader

  - by Iapilgrim

  Hi, I have the Hibernate model @Cache(usage = CacheConcurrencyStrategy.NONE, region = SitesConstants.CACHE_REGION) public class Node extends StatefulEntity implements Inheritable, Cloneable { private Node _parent; private List<Node> _childNodes; .. } @Cache(usage = CacheConcurrencyStrategy.NONE, region = SitesConstants.CACHE_REGION) public class Page extends Node implements Defaultable, Securable { private RootZone _rootZone; ...... @OneToOne(fetch = FetchType.LAZY) @JoinColumn(name = "root_zone_id", insertable = false, updatable = false) public RootZone getRootZone() { return _rootZone; } public void setRootZone(RootZone rootZone) { if (rootZone != null) { rootZone.setPageId(this.getId()); _rootZone = rootZone; } } I want to get all pages ( call getSiteTree), so I using this query String hpql = "SELECT n FROM Node n "; See the trace I find Page.setRootZone(RootZone) line: 155 NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not available [native method] NativeMethodAccessorImpl.invoke(Object, Object[]) line: 39 DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25 Method.invoke(Object, Object...) line: 597 BasicPropertyAccessor$BasicSetter.set(Object, Object, SessionFactoryImplementor) line: 66 PojoEntityTuplizer(AbstractEntityTuplizer).setPropertyValues(Object, Object[]) line: 352 PojoEntityTuplizer.setPropertyValues(Object, Object[]) line: 232 SingleTableEntityPersister(AbstractEntityPersister).setPropertyValues(Object, Object[], EntityMode) line: 3580 TwoPhaseLoad.initializeEntity(Object, boolean, SessionImplementor, PreLoadEvent, PostLoadEvent) line: 152 QueryLoader(Loader).initializeEntitiesAndCollections(List, Object, SessionImplementor, boolean) line: 877 QueryLoader(Loader).doQuery(SessionImplementor, QueryParameters, boolean) line: 752 QueryLoader(Loader).doQueryAndInitializeNonLazyCollections(SessionImplementor, QueryParameters, boolean) line: 259 QueryLoader(Loader).doList(SessionImplementor, QueryParameters) line: 2232 QueryLoader(Loader).listIgnoreQueryCache(SessionImplementor, QueryParameters) line: 2129 QueryLoader(Loader).list(SessionImplementor, QueryParameters, Set, Type[]) line: 2124 QueryLoader.list(SessionImplementor, QueryParameters) line: 401 QueryTranslatorImpl.list(SessionImplementor, QueryParameters) line: 363 HQLQueryPlan.performList(QueryParameters, SessionImplementor) line: 196 SessionImpl.list(String, QueryParameters) line: 1149 QueryImpl.list() line: 102 QueryImpl.getResultList() line: 67 NodeDaoImpl.getSiteTree(long) line: 358 PageNodeServiceImpl.getSiteTree(long) line: 797 NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not available [native method] NativeMethodAccessorImpl.invoke(Object, Object[]) line: 39 DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25 Method.invoke(Object, Object...) line: 597 AopUtils.invokeJoinpointUsingReflection(Object, Method, Object[]) line: 307 JdkDynamicAopProxy.invoke(Object, Method, Object[]) line: 198 $Proxy100.getSiteTree(long) line: not available the calling setRootZone in Page makes Hibernate issue a hit to database. I don't want this. So my question is + Why query String hpql = "SELECT n FROM Node n "; issues un-expected trace logs like above. Why the query String hpql = "SELECT n.nodename FROM Node n " not? What is the mechanism behind? Note: Im using hibernate caching level 2. In case I don't want to see that trace logs. I mean I just get Node data only. How to do ? Thanks for your help. Sorry for my bad english :( Van

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• ASP.Net Layered app - Share Entity Data Model amongst layers

  - by Chris Klepeis

  How can I share the auto-generated entity data model (generated object classes) amongst all layers of my C# web app whilst only granting query access in the data layer? This uses the typical 3 layer approach: data, business, presentation. My data layer returns an IEnumerable<T> to my business layer, but I cannot return type T to the presentation layer because I do not want the presentation layer to know of the existence of the data layer - which is where the entity framework auto-generated my classes. It was recommended to have a seperate layer with just the data model, but I'm unsure how to seperate the data model from the query functionality the entity framework provides.

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• PHP sessions and class members.

  - by JDW

  Ok, messing about with classes in PHP and can't get it to work the way I'm used to as a C++/Java-guy. In the "_init" funtion, if I run a query at the "// query works here" line", everythong works, but in the "getUserID" function, all that happens is said warning... "getUserID" gets called from login.php (they are in the same dir): login.php <?php include_once 'sitehandler.php'; include_once 'dbhandler.php'; session_start(); #TODO: Safer input handling $t_userName = $_POST["name"]; $t_userId = $_SESSION['handler']['db']->getUserID($t_userName); if ($t_userId != -1) { $_SESSION['user']['name'] = $t_userName; $_SESSION['user']['id'] = $t_userId; } //error_log("user: " . $_SESSION['user']['name'] . ", id: ". $_SESSION['user']['id']); header("Location: " . $_SERVER["HTTP_REFERER"]); ? dbhandler.php <?php include_once 'handler.php'; class DBHandler extends HandlerAbstract { private $m_handle; function __construct() { parent::__construct(); } public function test() { #TODO: isdir liquibase #TODO: isfile liquibase-195/liquibase + .bat + execrights $this->m_isTested = true; } public function _init() { if (!$this->isTested()) $this->test(); if (!file_exists('files/data.db')) { #TODO: How to to if host is Windows based? exec('./files/liquibase-1.9.5/liquibase --driver=org.sqlite.JDBC --changeLogFile=files/data_db.xml --url=jdbc:sqlite:files/data.db update'); #TODO: quit if not success } #TODO: Set with default data try { $this->m_handle = new SQLite3('files/data.db'); } catch (Exception $e) { die("<hr />" . $e->getMessage() . "<hr />"); } // query works here $this->m_isSetup = true; } public function teardown() { } public function getUserID($name) { // PHP Warning: SQLite3::prepare(): The SQLite3 object has not been correctly initialised in $t_statement = $this->m_handle->prepare("SELECT id FROM users WHERE name = :name"); $t_statement->bindValue(":name", $name, SQLITE3_TEXT); $t_result = $t_statement->execute(); //var_dump($this->m_handle); return ($t_result)? (int)$t_result['id']: -1; } }

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