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• Efficient way to access a mapping of identifiers in Python

  - by sixbelo

  I am writing an app to do a file conversion and part of that is replacing old account numbers with a new account numbers. Right now I have a CSV file mapping the old and new account numbers with around 30K records. I read this in and store it as dict and when writing the new file grab the new account from the dict by key. My question is what is the best way to do this if the CSV file increases to 100K+ records? Would it be more efficient to convert the account mappings from a CSV to a sqlite database rather than storing them as a dict in memory?

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• I need to create a contest....

  - by creocare

  I'm working on a contest where users vote for contestants. Each contestant will have a bio. I was wondering what would be the best way to approach this? Should I do this in php or javascript? Should I use a database to collect data? Should I use sqlite3? If I use sqlite3 how do i install that on my mac? I'm very new to all this but I'm a quick learner. Thanks for any advice.

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• How to design the application to conform to the n-tier architecture? (Winform sample in .net with li

  - by AlexRednic

  Rather a simple question. But the implications are vast. Over the last few weeks I've been reading a lot of material about n-tier architecture and it's implementation in the .NET world. The problem is I couldn't find a relevant sample for Winforms with Linq (linq is the way to go for BLL right?). How did you guys manage to grasp the n-tier concept? Books, articles, relevant samples etc.

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• Crash when checking BOF property of pessimistic locked ADO recordset

  - by Patrick

  Bit of an odd one for you: I've got two connections to a database, on one I've opened a _RecordsetPtr with a pessimistic lock. I can no longer send an UPDATE command on the other connection. I can send a SELECT command on the second connection and data is returned. If I use a read only lock then there are no problems however when I use a pessimistic lock on the second connection as well I can check the State == adStateOpen but the program hangs when I test the BOF property! If I don't test the BOF property and try to call moveNext on the second connection the software hangs If I do neither of these I am able to access the data via the second connection but trying to access the data from the first connection causes the software to hang. Any one seen anything similar as I'm a bit stuck? EDIT : it wasn't hanging, someone had put a 30 minute timeout on the connection and I wasn't waiting that long while testing...

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• T-SQL Self Join in combination with aggregate function

  - by Nick

  Hi, i have the following table. CREATE TABLE [dbo].[Tree]( [AutoID] [int] IDENTITY(1,1) NOT NULL, [Category] [varchar](10) NULL, [Condition] [varchar](10) NULL, [Description] [varchar](50) NULL, CONSTRAINT [PK_Tree] PRIMARY KEY CLUSTERED ( [AutoID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] GO the data looks like this: INSERT INTO [Test].[dbo].[Tree] ([Category] ,[Condition] ,[Description]) VALUES ('1','Alpha','Type 1') INSERT INTO [Test].[dbo].[Tree] ([Category] ,[Condition] ,[Description]) VALUES ('1','Alpha','Type 1') INSERT INTO [Test].[dbo].[Tree] ([Category] ,[Condition] ,[Description]) VALUES ('2','Alpha','Type 2') INSERT INTO [Test].[dbo].[Tree] ([Category] ,[Condition] ,[Description]) VALUES ('2','Alpha','Type 2') go I try now to do the following: SELECT Category,COUNT(*) as CategoryCount FROM Tree where Condition = 'Alpha' group by Category but i wish also to get the Description for each Element. I tried several subqueries, self joins etc. i always come to the problem that the subquery cannot return more than one record. The problem is caused by a poor database design which i cannot change and i run out of ideas to get this done in a single query ;-(

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• Design pattern for data entry forms with LINQ2SQL

  - by petebob796

  I am about to start a new winforms data entry application, it already has the database designed which I am comfortable with. I was going to use LINQ2SQL to access the tables to keep things type safe but am now wondering about design patterns, something I am just getting into. Since LINQ is giving me objects to use should I still create classes in between to hold the validation code and helper methods or should these just go in with the UI? It just seems I will end up with classes sat in between with little code which will cause the UI classes to have code just getting and setting values in the intermediate class and returning from validation to flag errors... Any good reading on this? Should I consider the entity framework (or similar) instead?

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• How do online stores handle 2 customers that add the last item to their cart?

  - by Alex

  I'm making a store web app for a college class. I'm wondering what do stores like Amazon do when there is only 1 item left? Do they let multiple customers add the last item to their cart, and whoever checks out first gets it? Meaning that the inventory database is updated after purchase. or Do they let only one customer add the last item to their cart and remove the item from the inventory. If the customer's session times out, then the item is put back in the inventory.

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• Data not entering the table

  - by Luke

  //loop through usernames to add to league table for ($i = 0; $i < count($user); $i++) { //set some new variables in an array $username = $user[$i]; $squad = $team[$i]; //add details to league table if ( $username != "Ghost") { $database->addUsersToLeagueTable($username, $squad); } } I use this code to add to the league table, the following is more code: function addUsersToLeagueTable($username, $squad) { $q = "INSERT INTO `$_SESSION[comp_name]` ( `user` , `team` , `home_games_played` , `home_wins` , `home_draws` , `home_losses` ,`home_points, `home_goals_for` , `home_goals_against` , `away_games_played` , `away_wins` , `away_draws` , `away_losses` , `away_points` , `away_goals_for` , `away_goals_against` ) VALUES ( '$username', '$squad', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0')"; return mysql_query($q, $this->connection); } Can you see any obvious reason why this isn't happening? Thanks

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• when to use Hibernate vs. Simple ResultSets for small application

  - by luke

  I just started working on upgrading a small component in a distributed java application. The main application is a rather complicated applet/servlet combo running on JBoss and it extensively uses Hibernate for its DataAccess. The component i am working on however is very a very straightforward data importing service. Basically the workflow is Listen for a network event Parse the data packet, extract a set of identifiers Map the identifier set to a primary key in our database Parse the rest of the packet and insert items in a related table using the foreign key found in step 3 Repeat in the previous version of this component it used a hibernate based DAL, that is no longer usable for a variety of reasons (in particular it is EOL), so I am in charge of replacing the Data Access layer for this component. So on the one hand I think i should use Hibernate because that's what the rest of the application does, but on the other i think i should just use regular java.sql.* classes because my requirements are really straightforward and aren't expected to change any time soon. So my question is (and i understand it is subjective) at what point do you think that the added complexity of using an ORM tool (in terms of configuration, dependencies...) is worth it? UPDATE due to the way the DataAccesLayer for the main application was written (weird dependencies) i cannot easily use it, i would have to implement it myself.

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• Oracle Query Optimization: Why is My Second Query Faster?

  - by Patrick Cuff

  I was having some performance issues with an Oracle query, so I downloaded a trial of the Quest SQL Optimizer for Oracle, which made some changes that dramatically improved the query's performance. I'm not exactly sure why the recommended query had such an improvement; can anyone provide an explanation? Before: SELECT t1.version_id, t1.id, t2.field1, t3.person_id, t2.id FROM table1 t1, table2 t2, table3 t3 WHERE t1.id = t2.id AND t1.version_id = t2.version_id AND t2.id = 123 AND t1.version_id = t3.version_id AND t1.VERSION_NAME <> 'AA' order by t1.id Plan Cost: 831 Elapsed Time: 00:00:21.40 Number of Records: 40,717 After: SELECT /*+ USE_NL_WITH_INDEX(t1) */ t1.version_id, t1.id, t2.field1, t3.person_id, t2.id FROM table2 t2, table3 t3, table1 t1 WHERE t1.id = t2.id + 0 AND t1.version_id = t2.version_id + 0 AND t2.id = 123 AND t1.version_id = t3.version_id + 0 AND t1.VERSION_NAME || '' <> 'AA' AND t3.version_id = t2.version_id + 0 order by t1.id Plan Cost: 686 Elapsed Time: 00:00:00.95 Number of Records: 40,717 Questions: Why does re-arranging the order of the tables in the FROM clause help? Why does adding + 0 to the WHERE clause comparisons help? Why does || '' <> 'AA' in the WHERE clause VERSION_NAME comparison help? Is this a more efficient way of handling possible nulls on this column?

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• Get top 'n' records by report_id

  - by Skudd

  I have a simple view in my MSSQL database. It consists of the following fields: report_id INT ym VARCHAR -- YYYY-MM keyword VARCHAR(MAX) visits INT I can easily get the top 10 keyword hits with the following query: SELECT TOP 10 * FROM top_keywords WHERE ym BETWEEN '2010-05' AND '2010-05' ORDER BY visits DESC Now where it gets tricky is where I have to get the top 10 records for each report_id in the given date range (ym BETWEEN @start_date AND @end_date). How would I go about getting the top 10 for each report_id? I've stumbled across suggestions involving the use of ROW_NUMBER() and RANK(), but have been vastly unsuccessful in their implementation.

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• How to query an XML File with E4X in AS3?

  - by yens resmann

  I need to archive a database-driven flash as3 website. I exported a table to xml so now i have something like this: <RECORDS> <RECORD> <id>home</id> <msg>bodytext</msg> <type>0</type> <lastEditDate>0000/0/0 00:00:00</lastEditDate> <lastAccessDate>2009/6/17 11:37:21</lastAccessDate> <timesAccessed>855</timesAccessed> </RECORD> <RECORD> <id>contact</id> <msg>contact body text</msg> <type>0</type> <lastEditDate>0000/0/0 00:00:00</lastEditDate> <lastAccessDate>2010/5/6 20:40:46</lastAccessDate> <timesAccessed>831</timesAccessed> </RECORD> </RECORDS> Now I would like to select the RECORD where id is set to home. In SQL: SELECT * FROM table WHERE id='home' How can i do the same thing with E4X for AS3 ?

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• Replace data in MySQL table with data from another table

  - by Oli

  I am trying to modify an existing MySQL database for use in a new application. I have a table of items (table_items), which has multiple fields, including "ItemID" and "ItemName". I have another table (table_list) which has "ItemName" in it, but no ItemID. I need to either update this table to contain ItemID instead of ItemName, or create a new table which imports ItemIDs from table_items as opposed to the ItemName when table_list.ItemName = table_items.ItemName. I have tried the following: UPDATE table_list A, table_items B SET A.ItemName = B.ItemID WHERE A.ItemName = B.ItemName The current table has over 500,000 rows and every time i try this in PHPMyAdmin i get the error "the MySQl server has gone away". Any help greatly appreciated.

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• Results from two queries at once in sqlite?

  - by SF.

  I'm currently trying to optimize the sluggish process of retrieving a page of log entries from the SQLite database. I noticed I almost always retrieve next entries along with count of available entries: SELECT time, level, type, text FROM Logs WHERE level IN (%s) ORDER BY time DESC, id DESC LIMIT LOG_REQ_LINES OFFSET %d* LOG_REQ_LINES ; together with total count of records that can match current query: SELECT count(*) FROM Logs WHERE level IN (%s); (for a display "page n of m") I wonder, if I could concatenate the two queries, and ask them both in one sqlite3_exec() simply concatenating the query string. How should my callback function look then? Can I distinguish between the different types of data by argc? What other optimizations would you suggest?

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• Visual Studio 2010 deploys views too late in deploy process

  - by Markus

  I have a database project in my VS2010 solution. I recently changed a view and and changed a number of functions to use this view instead of going directly against a table. But now when I deploy I get errors on most of these functions because the column asked for does not exists in the view yet. The update of the view happends later than the update of UDF's. Is there any way to change this behaviour? Wouldn't the best thing be if the deploy script updated in this order: tables, views, SP and UDF. It seems like tables is updated first, but the views are just thrown in somewhere in the middle of the deploy script.

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• Best practice for avoiding locks on a heavily read table?

  - by Luiggi

  Hi, I have a big database (~4GB), with 2 large tables (~3M records) having ~180K SELECTs/hour, ~2k UPDATEs/hour and ~1k INSERTs+DELETEs/hour. What would be the best practice to guarantee no locks for the reading tasks while inserting/updating/deleting? I was thinking about using a NOLOCK hint, but there is so much discussed about this (is good, is bad, it depends) that I'm a bit lost. I must say I've tried this in a dev environment and I didn't find any problems, but I don't want to put it on production until I get some feedback... Thank you! Luiggi

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• Delphi - change text color based on current record value

  - by Welliam

  using db controls connected to a FireBird database. and I have a simple dblabel I want to change text color based on current value for current record The user navigate using the dbnavigator and I wrote code in the navigator button click. but there is a problem the code always read the previous record value not the current one so the color is wrong !! for example: procedure <navigator button click>; begin if table1.FieldByName('field1').AsString = 'val1' then <dblabel.textcolor> := red else <dblabel.textcolor> := green; end; but as I said the value is one record behind. why is that and what is the best approach to change label text color ? Thanks

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• Storing Values in colunms alphabetic?

  - by Mdillion

  Is there any benefit to storing content alphabetic in columns? Maybe make lookups faster? If yes then when i add new lookup values to my tables do i need to rebuild the PK for the looup values to fit in the new text? Say a table like this: City_tbl city_id: example: 1120 City_name: example: New York. If I need to add Chicago to it, do i add it at the bottom of the list with the next ID which may be 2000 or do i inset it after the city in alphabetic order which would mean I need to update the PK Id of all following IDs by 1. Only benefit I know about is when I have to manually add lookup values without quering the database I can quickly check the lookup value list for exiting items with ease. But not sure if it may make lookups faster or something if the system knows the text is in aplhabetic order.

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• To use an api or store a large dataset in a rails app?

  - by Dave

  Hi all- I am working on a site that has the potential to need a LOT of space. Basically we hope to have every video game every created stored in a database along with an image of the cover. There are some api's out there that might be able to help, like GiantBomb's (www.giantbomb.com). We are trying to decide whether to store the data locally and if so where to find that comprehensive a list, or make calls to the api on demand. The problem with the latter is likely latency and also downtime problems. Assuming we want to store it locally here are the questions: 1) Where can we find this kind of data (yes, I looked on google, and no I couldnt find anything:)) 2) What is the most efficient way to encode and store the images? Thanks!

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• Do partitions allow multiple bulk loads?

  - by ck

  I have a database that contains data for many "clients". Currently, we insert tens of thousands of rows into multiple tables every so often using .Net SqlBulkCopy which causes the entire tables to be locked and inaccessible for the duration of the transaction. As most of our business processes rely upon accessing data for only one client at a time, we would like to be able to load data for one client, while updating data for another client. To make things more fun, all PKs, FKs and clustered indexes are on GUID columns (I am looking at changing this). I'm looking at adding the ClientID into all tables, then partitioning on this. Would this give me the functionality I require?

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• Getting age from an encrypted DOB field

  - by Mailforbiz

  Hi all Due to certain compliance requirements, we have to encrypt the user DOB field in the database. We also have another requirement to be able to search a user by his age. Our DB doesn't support transparent encryption so encryption will handled by the application. Any good ideas on how to allow for searching by age? One thought is to save the YOB in a separate column in cleartext and still be able to comply to our compliance requirement. Aside from that, any other design strategy that would help? Thanks in advance!

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• getting double value from group concact

  - by Sackling

  I am having a problem where I am getting duplicated values from what I think I should be getting. here is my sql: SELECT DISTINCT p.products_image, pd.products_name, p.products_id, p.products_model, p.manufacturers_id, m.manufacturers_name, p.products_price, p.products_sort_order, p.products_tax_class_id, pd.products_viewed, group_concat(p2i.icons_id separator ",") AS icon_ids, group_concat(pi.icon_class separator ",") AS icon_class, IF(s.status, s.specials_new_products_price, NULL) AS specials_new_products_price, IF(s.status, s.specials_new_products_price, p.products_price) AS final_price FROM products p LEFT JOIN specials s ON p.products_id = s.products_id LEFT JOIN manufacturers m ON p.manufacturers_id = m.manufacturers_id JOIN products_description pd ON p.products_id = pd.products_id JOIN products_to_categories p2c ON p.products_id = p2c.products_id INNER JOIN products_specifications ps7 ON p.products_id = ps7.products_id LEFT JOIN products_to_icon p2i ON p.products_id = p2i.products_id LEFT JOIN products_icons pi ON p2i.icons_id = pi.icons_id WHERE p.products_status = '1' AND pd.language_id = '1' AND ps7.specification IN ('Polycotton' , 'Reflective') AND ps7.specifications_id = '7' AND ps7.language_id = '1' AND p2c.categories_id = '21' GROUP BY p.products_id ORDER BY p.products_sort_order The column that is getting double values is icon_ids from the group concact. This seams to happen only if ploycotton, and reflective are both IN ps7.specification. If it is only one or the other then it works fine. The products_to_icon table contains 2 columns, products_id and icons_id. If a product has 2 icons, there are 2 rows so I'm pretty sure it is this fact that is causing the duplicate icons ids. When I run this, the icon_ids column for a product with 2 icons is "4,4,6,6" for example, when what I need is "4,6"

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• Adding Related Entities without using navigation properties

  - by Barisa Puter

  I have the following classes, set for testing: public class Company { [DatabaseGenerated(DatabaseGeneratedOption.Identity)] public int Id { get; set; } public string Name { get; set; } } public class Employee { [DatabaseGenerated(DatabaseGeneratedOption.Identity)] public int Id { get; set; } public string Name { get; set; } public int CompanyId { get; set; } public virtual Company Company { get; set; } } public class EFTestDbContext : DbContext { public DbSet<Employee> Employees { get; set; } public DbSet<Company> Companies { get; set; } } For the sake of testing, I wanted to insert one company and one employee for that company with single SaveChanges call, like this: Company company = new Company { Name = "Sample company" }; context.Companies.Add(company); // ** UNCOMMENTED FOR TEST 2 //Company company2 = new Company //{ // Name = "Some other company" //}; //context.Companies.Add(company2); Employee employee = new Employee { Name = "Hans", CompanyId = company.Id }; context.Employees.Add(employee); context.SaveChanges(); Even though I am not using navigational properties, but instead I've made relation over Id, this somehow mysteriously worked - employee was saved with proper foreign key to company which got updated from 0 to real value, which made me go ?!?! Some hidden C# feature? Then I've decided to add more code, which is commented in the snippet above, making it to be inserting of 2 x Company entity and 1 x Employee entity, and then I got exception: Unable to determine the principal end of the 'CodeLab.EFTest.Employee_Company' relationship. Multiple added entities may have the same primary key. Does this mean that in cases where foreign key is 0, and there is a single matching entity being inserted in same SaveChanges transaction, Entity Framework will assume that foreign key should be for that matching entity? In second test, when there are two entities matching the relation type, Entity Framework throws an exception as it is not able to figure out to which of the Companies Employee should be related to.

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• submit in html on sql query

  - by user1644661

  i need to run this sql query , which give me a list of Id and Dates i want to click each result and take with me the Id value to the next form i wrote this query above but i see in the debager that the hidden ID get his value but not pass to the next form i think i have a problem with the submit() . where should i put him ? thanks anat function ShowAllCarts($user_email) { $connB = new ProductDAO(); $connB->Connect(); $pro_query = "SELECT * FROM Cart WHERE `Email`='$user_email';"; $db_result = $connB->ExecSQL($pro_query); $html_result = '<div data-role="content"> <ul data-role="listview" data-theme="b"> '; $html_result .= '<form action="PreviouscartProduct.php" method="POST"/>'; while($row_array = $db_result->fetch_array(MYSQLI_ASSOC)) { $Id= $row_array['Id']; $Date= $row_array['Date']; //$html_result // $html_result .="<li><a href='PreviouscartProduct.php'>Cart number: $Id from Date: $Date><input type='hidden' name='Id' value'<?=$Id?>'</input></a></li>'"; $html_result .= '<a onclick="this.form.submit();" </a>; } $html_result .= ' </ul> </div>'; $html_result .= '</form>'; $connB->Disconnect(); return $html_result; } //display all carts $func_result = ShowAllCarts($Email);

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• Data access layer design

  - by Sam

  I have a web app and a console application accessing a db. The db has 2 tables (A, B) one of which (A) is specific to the web app. When writing a data access layer, what is the best way to do it? Technically data access layer should provide access to all the data accessible. In doing so, methods to interact with A are exposed to the console application if we have single access layer. Does creating 2 access layers to 2 table in the same database makes any sense? What is a good way to do it?

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