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• Database structure for storing Bank-like accounts and transactions

  - by user1241320

  We're in the process of adding a bank-like sub-system to our own shop. We already have customers, so each will be given a sort of account and transactions of some kind will be possible (adding to the account or subtracting from it). So we at least need the account entity, the transaction one and operations will then have to recalculate overall balances. How would you structure your database to handle this? Is there any standard bank system have to use that I could mock? By the way, we're on mysql but will also look at some nosql solution for performance boost.

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• Compiled query using list of class objects in C#

  - by Sukan

  Hello , Can somebody help me out in creating compiled queries where input is to be a list of class objects? I have seen examples where Func<DataContext, somematchobject, IQueryable<T>> is created and compiled. But can I do something like Func<List<T>, matchObject, T>, and compile it? Basically I want an object(T) meeting certain conditions (as in matchObject) to be returned from a list of objects(List<T>). Will CompiledQuery.Compile help me in this? Please help me experts!!

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• What is the benefit of using int instead of bigint in this case?

  - by Yeti

  (MYSQL n00b) I have 3 tables: id = int(10), photo_id = bigint(20) PHOTO records limited to 3 million PHOTO: +-------+-----------------+ | id | photo_num | +-------+-----------------+ | 1 | 123456789123 | | 2 | 987654321987 | | 3 | 5432167894321 | +-------+-----------------+ COLOR: +-------+-----------------+---------+ | id | photo_num | color | +-------+-----------------+---------+ | 1 | 123456789123 | red | | 2 | 987654321987 | blue | | 3 | 5432167894321 | green | +-------+-----------------+---------+ SIZE: +-------+-----------------+---------+ | id | photo_num | size | +-------+-----------------+---------+ | 1 | 123456789123 | large | | 2 | 987654321987 | small | | 3 | 5432167894321 | medium | +-------+-----------------+---------+ Both COLOR and SIZE tables will have several million records. Q1: Is it better to change photo_num on COLOR and SIZE to int(10) and point it to PHOTO's id? Right now I use these: (PHOTO is no where in the picture) SELECT * from COLOR WHERE photo_num='xxx'; SELECT * from SIZE WHERE photo_num='xxx'; Q2: How will the SELECT query look if PHOTO id was used in COLOR, SIZE?

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• validate linqtosql mapping to a model

  - by Coppermill

  I have generated a LinqtoSQL mapping xml file, which I have a valid XSD schema that I check to make sure the XML is correct. Now I want to check that the field type match the Model/Interface for example: checking that the nullable fields are nullable that int are int etc anyone got any ideas if I can do this?

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• Loading a DB table into nested dictionaries in Python

  - by Hossein

  Hi, I have a table in MySql DB which I want to load it to a dictionary in python. the table columns is as follows: id,url,tag,tagCount tagCount is the number of times that a tag has been repeated for a certain url. So in that case I need a nested dictionary, in other words a dictionary of dictionary, to load this table. Because each url have several tags for which there are different tagCounts.the code that I used is this:( the whole table is about 22,000 records ) cursor.execute( ''' SELECT url,tag,tagCount FROM wtp ''') urlTagCount = cursor.fetchall() d = defaultdict(defaultdict) for url,tag,tagCount in urlTagCount: d[url][tag]=tagCount print d first of all I want to know if this is correct.. and if it is why it takes so much time? Is there any faster solutions? I am loading this table into memory to have fast access to get rid of the hassle of slow database operations, but with this slow speed it has become a bottleneck itself, it is even much slower than DB access. and anyone help? thanks

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• Speed up multiple JDBC SQL querys?

  - by paddydub

  I'm working on a shortest path a* algorithm in java with a mysql db. I'm executing the following SQL Query approx 300 times in the program to find route connections from a database of 10,000 bus connections. It takes approx 6-7 seconds to execute the query 300 times. Any suggestions on how I can speed this up or any ideas on a different method i can use ? Thanks ResultSet rs = stmt.executeQuery("select * from connections" + " where Connections.From_Station_stopID ="+StopID+";"); while (rs.next()) { int id = rs.getInt("To_Station_id"); String routeID = rs.getString("To_Station_routeID"); Double lat = rs.getDouble("To_Station_lat"); Double lng = rs.getDouble("To_Station_lng"); int time = rs.getInt("Time"); }

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• Query to retrieve records by aplhabetic order, except for n predefined items which must be on top

  - by Ashraf Bashir

  I need to retrieve all records ordered alphabetically. Except for a predefined list of record's columns which their records should appear first in a given predefined order, then all other records should be sorted alphabetically based on the same column For instance, assume we have the following table which is called Names Lets assume the predefined list is ("Mathew", "Ashraf", "Jack"). I.e. these are the names of whom their records should be listed first as in the predefined order. So the desired query result should be: Which query could retrieve this custom order ? P.S, I'm using MySQL. Here's my trial based on comments' request: (SELECT * FROM Names WHERE Name in ('Mathew', 'Ashraf', 'Jack')) UNION (SELECT * FROM Names WHERE Name NOT IN ('Mathew', 'Ashraf', 'Jack') ORDER BY Name ASC); the first query result wasn't ordered as required.

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• Working with foreign keys - cannot insert

  - by Industrial

  Hi everyone! Doing my first tryouts with foreign keys in a mySQL database and are trying to do a insert, that fails for this reason: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails Does this mean that foreign keys restrict INSERTS as well as DELETES and/or UPDATES on each table that is enforced with foreign keys relations? Thanks! Updated description: Products ---------------------------- id | type ---------------------------- 0 | 0 1 | 3 ProductsToCategories ---------------------------- productid | categoryid ---------------------------- 0 | 0 1 | 1 Product table has following structure CREATE TABLE IF NOT EXISTS `alpha`.`products` ( `id` MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT , `type` TINYINT(2) UNSIGNED NOT NULL DEFAULT 0 , PRIMARY KEY (`id`) , CONSTRAINT `prodsku` FOREIGN KEY (`id` ) REFERENCES `alpha`.`productsToSku` (`product` ) ON DELETE CASCADE, ON UPDATE CASCADE) ENGINE = InnoDB;

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• Refactoring - Speed increase

  - by Michael G

  How can I make this function more efficient. It's currently running at 6 - 45 seconds. I've ran dotTrace profiler on this specific method, and it's total time is anywhere between 6,000ms to 45,000ms. The majority of the time is spent on the "MoveNext" and "GetEnumerator" calls. and example of the times are 71.55% CreateTableFromReportDataColumns - 18, 533* ms - 190 calls -- 55.71% MoveNext - 14,422ms - 10,775 calls What can I do to speed this method up? it gets called a lot, and the seconds add up: private static DataTable CreateTableFromReportDataColumns(Report report) { DataTable table = new DataTable(); HashSet<String> colsToAdd = new HashSet<String> { "DataStream" }; foreach (ReportData reportData in report.ReportDatas) { IEnumerable<string> cols = reportData.ReportDataColumns.Where(c => !String.IsNullOrEmpty(c.Name)).Select(x => x.Name).Distinct(); foreach (var s in cols) { if (!String.IsNullOrEmpty(s)) colsToAdd.Add(s); } } foreach (string col in colsToAdd) { table.Columns.Add(col); } return table; }

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• Read binary data from a MDB-file running under LAMP

  - by BusterX

  I need to be able to connect to an MDB-file in a LAMP-environment (running on Linux) and ultimately insert converted data into a Mysql db. The data I need to access is stored as a BLOB (Long Binary Data according to Access) in the MDB file. I have not yet been able to actually have a look at the data but I have been told that the BLOB consists of byte strings. Something along the lines of: 0x1c 0x10 0x27 0x00 0x00 I need to parse the byte strings and convert these to a format that is human readable. I do have access to the documentation that explains the various byte strings. So this is really two questions: How do a get access to the MDB file via PHP* (running under LAMP) and read the BLOB (I do not have access to a Windows-platform)? What would be the best way to parse the binary data (in PHP*) once I am able to connect to the MDB-file? *Or are there other methods/languages that are more appropriate?

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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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• How to insert multiple check-box values inside database when one or more will be left unchecked?

  - by Sally

  I have a form that contains 5 check boxes. The user may select one or more of these check boxes. The user may select 2 and leave 3 unchecked or select 4 and leave one unchecked and so on, in that case how can I write the php/mysql code that will insert the form data into the database. With just one selection it's easy, I would do: $checkbox_value = $_POST['i_agree']; mysql_query("INSERT INTO terms (user, pass, conditions) VALUES ('$user','$pass','$checkbox_value')"); But how can I write this when there are multiple check box options and only one or more of them will be checked? I want to insert them all in one column called "tags" separated by commas.

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• C# Entity Framework Base Repository

  - by Andy

  I'm trying to create a base repository for use with Entity Framework 4.0 and having some trouble. In this code below, why is it not possible to do this in one line? public IEnumerable<T> GetAll<T>(Expression<Func<T, bool>> filter) { IEnumerable<T> allCustomers = this.GetAll<T>(); IEnumerable<T> result = allCustomers.Where(filter.Compile()); return result; } Won't this result in 2 SQL statements: one without a where clause that retrieves all rows, and one with a where clause that only retrieves the rows that match the predicate? How can this be done with a single SQL statement? I can't get it to compile if I try to cast the filter.Compile() to Func<Customer, bool>. Thanks, Andy

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• Find Elements by Attribute using XDocument

  - by Ignacio

  This query seems to be valid, but I have 0 results. IEnumerable<XElement> users = (from el in XMLDoc.Elements("Users") where (string)el.Attribute("GUID") == userGUID.ToString() select el); My XML is as follows: <?xml version="1.0" encoding="utf-8" standalone="yes"?> <Users> <User GUID="68327fe2-d6f0-403b-a7b6-51860fbf0b2f"> <Key ID="F7000012ECEAD101"> ... </Key> </User> </Users> Do you have any clues to shed some light onto this?

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• Left Join not returning all rows

  - by DisgruntledGoat

  I have this query in MySQL: SELECT pr.*, pr7.value AS `room_price_high` FROM `jos_hp_properties` pr LEFT OUTER JOIN `jos_hp_properties2` pr7 ON pr7.property=pr.id WHERE pr7.field=23 The jos_hp_properties table has 27 rows but the query only returns one. Based on this question I think it may be because of the WHERE clause. The jos_hp_properties2 table has fields id, property, field, value, where field is a foreign key to a third table (which I don't need to get data from). Is there a way to select all the rows from the first table, including the value from table #2 where the field is 23 (or NULL if there is no field 23)?

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• Question about joins and table with Millions of rows

  - by xRobot

  I have to create 2 tables: Magazine ( 10 millions of rows with these columns: id, title, genres, printing, price ) Author ( 180 millions of rows with these columns: id, name, magazine_id ) . Every author can write on ONLY ONE magazine and every magazine has more authors. So if I want to know all authors of Motors Magazine, I have to use this query: SELECT * FROM Author, Magazine WHERE ( Author.id = Magazine.id ) AND ( genres = 'Motors' ) The same applies to Printing and Price column. To avoid these joins with tables of millions of rows, I thought to use this tables: Magazine ( 10 millions of rows with this column: id, title, genres, printing, price ) Author ( 180 millions of rows with this column: id, name, magazine_id, genres, printing, price ) . and this query: SELECT * FROM Author WHERE genres = 'Motors' Is it a good approach ? I can use Postgresql or Mysql.

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• Does a TransactionScope that exists only to select data require a call to Complete()

  - by fordareh

  In order to select data from part of an application that isn't affected by dirty data, I create a TransactionScope that specifies a ReadUncommitted IsolationLevel as per the suggestion from Hanselman here. My question is, do I still need to execute the oTS.Complete() call at the end of the using block even if this transaction scope was not built for the purpose of bridging object dependencies across 2 databases during an Insert, Update, or Delete? Ex: List<string> oStrings = null; using (SomeDataContext oCtxt = new SomeDataContext (sConnStr)) using (TransactionScope oTS = new TransactionScope(TransactionScopeOption.Required, new TransactionOptions { IsolationLevel = System.Transactions.IsolationLevel.ReadUncommitted })) { oStrings = oCtxt.EStrings.ToList(); oTS.Complete(); }

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• How can I pass in a params of Expression<Func<T, object>> to a method?

  - by Pure.Krome

  Hi folks, I have the following two methods :- public static IQueryable<T> IncludeAssociations<T>(this IQueryable<T> source, params string[] associations) { ... } public static IQueryable<T> IncludeAssociations<T>(this IQueryable<T> source, params Expression<Func<T, object>>[] expressions) { ... } Now, when I try and pass in a params of Expression<Func<T, object>>[], it always calls the first method (the string[]' and of course, that value isNULL`) Eg. Expression<Func<Order, object>> x1 = x => x.User; Expression<Func<Order, object>> x2 = x => x.User.Passport; var foo = _orderRepo .Find() .IncludeAssociations(new {x1, x2} ) .ToList(); Can anyone see what I've done wrong? Why is it thinking my params are a string? Can I force the type, of the 2x variables?

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• What choices to make for an application backend

  - by Saif Bechan

  I am creating an web application and I at the point that i am starting to make backend choices. Now there are a lot of ways to go with this, so I am looking for some good points and back practices. Some of the question i have involve: Should i make a seperate table in the db for admin users Should i extend make some classes to load the admin data and the normal data, or make seperate classes for the admin section Where can i get some information on making different types of users Just some best practices for a backend My application is written in PHP with an MySQL database.

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• Meaning of tA tC and tP

  - by Greg Wiley

  If this is a duplicate I appoligize, but looking for two-letter strings is quite hard in any search. I'm looking for the meaning of tA tC and tP in the context of a mysql query. And in the spirit of "teaching a man how to fish" it would be great if you could point me in the right direction of where to find this info in the future. Edit: The Query $wpdb->get_row($wpdb->prepare("SELECT tA.* FROM ".AMYLITE_ADS." tA, ".AMYLITE_ADS_CAMPAIGNS." tC, ".AMYLITE_PACKAGES." tP WHERE tA.id=tC.ad_id AND tC.campaign_id=tP.campaign_id AND tP.zone_id=%d AND tP.date_end>CURDATE() GROUP BY tA.id ORDER BY RAND()", $zone->id));

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• tricky SQL when joining

  - by Erik

  I've two tables, shows and objects. I want to print out the latest objects, and the shownames for them. Right now I'm doing it this way: SELECT MAX(objects.id) as max_id, shows.name, shows.id FROM shows, objects WHERE shows.id = objects.showId GROUP BY shows.name however, if I also want to fetch the episode of the object I can't put it like SELECT object.episode [...], because then wont automatically select the object which is MAX(objects.id), so my question is how to do that? If you haven't already figured out my tables they're like this: Shows id name and also: Objects id name episode season showId Using MySQL. Thanks!

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• Accessing non-related entities in LinqToSql entity classes

  - by Chris Johnson

  In LinqToSql, if I want to access a non-related entity in an entity partial class, how do I do this without creating a new DataContext? Here's the scenario: I have the tables Client, IssueType and ClientIssueType. A Client may specify a list of IssueTypes if they do not want to use the default IssueTypes. I have the default IssueTypes in the ClientIssueType table with a ClientId of null. In my Client partial I'd like to try to retrieve all IssueTypes, and if none are found, return all default IssueTypes. The only way I can see of accessing the IssueTypes with a null ClientId is by accessing the table through a new DataContext, which is problematic once I want to start assigning them to Issues. Where am I going wrong?

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• Should I stick only to AWS RDS Automated Backup or DB Snapshots?

  - by James Wise

  I am using AWS RDS for MySQL. With it comes on backup, I understand that amazon provides two types of backup - automated backup and database (DB) snapshot. The difference is explain in here - http://aws.amazon.com/rds/faqs/#23. However, I am still confuse if should I stick to automated backup only or both automated and manual (db snapshots). What do you think guys? What's the setup of your own? I heard to others that automated backup is not reliable due to some unrecoverable database when the DB instance is crashed so the DB snapshots are the way to rescue you. If I will do daily DB snapshots as similar settings to automated backup, I have gonna pay much bunch of bucks. Hope anyone could enlighten me or advise me the right set up. Thanks. James

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• Generate dynamic UPDATE command from Expression<Func<T, T>>

  - by Rui Jarimba

  I'm trying to generate an UPDATE command based on Expression trees (for a batch update). Assuming the following UPDATE command: UPDATE Product SET ProductTypeId = 123, ProcessAttempts = ProcessAttempts + 1 For an expression like this: Expression<Func<Product, Product>> updateExpression = entity => new Product() { ProductTypeId = 123, ProcessAttempts = entity.ProcessAttempts + 1 }; How can I generate the SET part of the command? SET ProductTypeId = 123, ProcessAttempts = ProcessAttempts + 1

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• SQL to get friends AND friends of friends of a user

  - by Enrique

  My MySQL tables structure is like this. USER int id varchar username FRIEND_LIST int user_id int friend_id For each friend relationship I insert 2 records in FRIEND_LIST. If user 1 is friend of user 2 then the next rows are inserted into FRIEND_LIST 1,2 2,1 I want to get the friends and friends of friends of an specific user. The select should return columns a, b, c. a: user_id b: friend_id c: username (username of friend_id ) If 1 is friend of 2 and 3. 2 is friend of 3, 4 and 5 3 is friend of 5,6,7 Then the query to get 1's friends and friends of friends should return: 1 2 two 1 3 three 2 1 one 2 3 three 2 4 four 2 5 five 3 1 one 3 5 five 3 6 six 3 7 seven Can I get this rows with a single query?

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