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• DataContext Refresh and PropertyChanging & PropertyChanged Events

  - by Scott

  I'm in a situation where I am being informed from an outside source that a particular entity has been altered outside my current datacontext. I'm able to find the entity and call refresh like so MyDataContext.Refresh(RefreshMode.OverwriteCurrentValues, myEntity); and the properties which have been altered on the entity are updated correctly. However neither of the INotifyPropertyChanging INotifyPropertyChanged appear to be raised when the refresh occurs and this leaves my UI displaying incorrect information. I'm aware that Refresh() fails to use the correct property getters and setters on the entity to raise the change notification events, but perhaps there is another way to accomplish the same thing? Am I doing something wrong? Is there a better method than Refresh? If Refresh is the only option, does anyone have a work around?

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• Understand Sql Server connectionstring for asp.net

  - by Eatdoku

  Hi, I am trying to understand the differences between the following 2 connectionstrings. one uses servername\instancename and the other one uses the server ip address. Can I specify port number for "serverName\instanceName". I know you can specify port number for ip address, something like '10.0.0.1,xxx'. thanks, Server=myServerName\theInstanceName;Database=myDataBase;Trusted_Connection=True; Server=myServerAddress;Database=myDataBase;Trusted_Connection=True;

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• Spaced repetition (SRS) for learning

  - by Fredrik Johansson

  A client has asked me to add a simple spaced repeition algorithm (SRS) for an onlinebased learning site. But before throwing my self into it, I'd like to discuss it with the community. Basically the site asks the user a bunch of questions (by automatically selecting say 10 out of 100 total questions from a database), and the user gives either a correct or incorrect answer. The users result are then stored in a database, for instance: userid questionid correctlyanswered dateanswered 1 123 0 (no) 2010-01-01 10:00 1 124 1 (yes) 2010-01-01 11:00 1 125 1 (yes) 2010-01-01 12:00 Now, to maximize a users ability to learn all answers, I should be able to apply an SRS algorithm so that a user, next time he takes the quiz, receives questions incorrectly answered more often; than questions answered correctly. Also, questions that are previously answered incorrectly, but recently often answered correctly should occur less often. Have anyone implemented something like this before? Any tips or suggestions? Theese are the best links I've found: http://en.wikipedia.org/wiki/Spaced_repetition http://www.mnemosyne-proj.org/principles.php http://www.supermemo.com/english/ol/sm2.htm

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• Should I commit or rollback a transaction that creates a temp table, reads, then deletes it?

  - by Triynko

  To select information related to a list of hundreds of IDs... rather than make a huge select statement, I create temp table, insert the ids into it, join it with a table to select the rows matching the IDs, then delete the temp table. So this is essentially a read operation, with no permanent changes made to any persistent database tables. I do this in a transaction, to ensure the temp table is deleted when I'm finished. My question is... what happens when I commit such a transaction vs. let it roll it back? Performance-wise... does the DB engine have to do more work to roll back the transaction vs committing it? Is there even a difference since the only modifications are done to a temp table? Related question here, but doesn't answer my specific case involving temp tables: http://stackoverflow.com/questions/309834/should-i-commit-or-rollback-a-read-transaction

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• sql query - how to apply limit within group by

  - by Raj

  hey guys assuming i have a table named t1 with following fields: ROWID, CID, PID, Score, SortKey it has the following data: 1, C1, P1, 10, 1 2, C1, P2, 20, 2 3, C1, P3, 30, 3 4, C2, P4, 20, 3 5, C2, P5, 30, 2 6, C3, P6, 10, 1 7, C3, P7, 20, 2 what query do i write so that it applies group by on CID, but instead of returning me 1 single result per group, it returns me a max of 2 results per group. also where condition is score = 20 and i want the results ordered by CID and SortKey. If I had to run my query on above data, i would expect the following result: RESULTS FOR C1 - note: ROWID 1 is not considered as its score < 20 C1, P2, 20, 2 C1, P3, 30, 3 RESULTS FOR C2 - note: ROWID 5 appears before ROWID 4 as ROWID 5 has lesser value SortKey C2, P5, 30, 2 C2, P4, 20, 3 RESULTS FOR C3 - note: ROWID 6 does not appear as its score is less than 20 so only 1 record returned here C3, P7, 20, 2 IN SHORT, I WANT A LIMIT WITHIN A GROUP BY. I want the simplest solution and want to avoid temp tables. sub queries are fine. also note i am using sqlite for this

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• Queries with Multiple Constraints

  - by ANITHA

  I have the following tables and fields: +------------------+ +-------------------+ +---------------+ | Request | | RequestItem | | Item | +------------------+ +-------------------+ +---------------+ | + Requester_Name | | + Request_No | | + Item | +------------------+ +-------------------+ +---------------+ | + Request_No | | + Item | +------------------+ +-------------------+ I would like to filter the items which are selected under a particular request number, along with a specific requester name. How might I go about doing this?

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• mysql query for getting all messages that belong to user's contacts

  - by aharon

  So I have a database that is setup sort of like this (simplified, and in terms of the tables, all are InnoDBs): Users: contains based user authentication information (uid, username, encrypted password, et cetera) Contacts: contains two rows per relationship that exists between users as (uid1, uid2), (uid2, uid1) to allow for a good 1:1 relationship (must be mutual) between users Messages: has messages that consist of a blob, owner-id, message-id (auto_increment) So my question is, what's the best MySQL query to get all messages that belong to all the contacts of a specific user? Is there an efficient way to do this?

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• tsql : how to do a substring replace?

  - by phill

  goal: I have the string "1234432144" I want to only replace the first 2 4's with '10' so I would get '1231032144' Is there a way to do this in tsql? so far I have come up with the tsql substring() function substring('1234432144', 4, 2) which draws the 44 .. however how do i replace it within the existing string? If i wrap a replace function around it, it replaces all occurrences of 44 in the string. any ideas? thanks in advance.

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• How to switch from MSSQL to MySQL for using with Excel pivot

  - by Sim

  Hi all, I have a table that contains sales transaction (~20 mil rows). Previously I used MSSQL and export it to an Excel pivot. Data refresh took 10-15 minutes but still do-able. However, after I migrated to MySQL (using XamppLite & ODBC), it took forever to refresh the data in the Excel pivot. Maybe I didn't optimize the MySQL good enough ? Anyone can share some thoughts 'bout this ? Thanks

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• Search 2 Columns with 1 Input Field

  - by Norbert

  I have a db with two columns: first name and last name. The first name can have multiple words. Last name can contain hyphenated words. Is there a way to search both columns with only one input box? Database ID `First Name` `Last Name` 1 John Peter Doe 2 John Fubar 3 Michael Doe Search john peter returns id 1 john returns id 1,2 doe returns id 1,3 john doe returns id 1 peter john returns id 1 peter doe returns id 1 doe john returns id 1 I previously tried the following. Searching for John Doe: SELECT * FROM names WHERE ( `first` LIKE '%john%' OR `first` LIKE '%doe%' OR `last` LIKE '%john%' OR `last` LIKE '%doe%' ) which returns both 1 and 3

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• Can't figure out how to list all the people that don't live in same City as...

  - by AspOnMyNet

  I’d like to list all the people ( Person table ) that don’t live in same city as those cities listed in Location table. Thus, if Location table holds a record with City=’New York’ and State=’Moon’, but Person table holds a record with FirstName=’Someone’, City=’New York’ and Location=’Mars’, then Someone is listed in the resulting set, since she lives in New York located on Mars and not New York located on Moon, thus we’re talking about different cities with the same name. I tried solving it with the following query, but results are wrong: SELECT Person.FirstName, Person.LastName, Person.City, Person.State FROM Person INNER JOIN Location ON (Person.City <> Location.City AND Person.State = Location.State) OR (Person.City = Location.City AND Person.State <> Location.State) OR (Person.City <> Location.City AND Person.State <> Location.State) ORDER BY Person.LastName; Any ideas?

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• many-to-many query

  - by kofto4ka

  Hello, guys! I have a problem and I dont know what is better solution. Okay, I have 2 tables: posts(id, title), posts_tags(post_id, tag_id). I have next task: must select posts with tags ids for example 4, 10 and 11. Not exactly, post could have any other tags at the same time. So, how I could do it more optimized? Creating temporary table in each query? Or may be some kind of stored procedure? In the future, user could ask script to select posts with any count of tags (it could be 1 tag only or 10 at the same time) and I must be sure that method that I will choose would be the best method for my problem. Sorry for my english, thx for attention.

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• add row to a BindingSource gives different autoincrement value from whats saved into DB

  - by Ruben Trancoso

  I have a DataGridView that shows list of records and when I hit a insert button, a form should add a new record, edit its values and save it. I have a BindingSource bound to a DataGridView. I pass is as a parameter to a NEW RECORD form so // When the form opens it add a new row and de DataGridView display this new record at this time DataRowView currentRow; currentRow = (DataRowView) myBindindSource.AddNew(); when user confirm to save it I do a myBindindSource.EndEdit(); // inside the form and after the form is disposed the new row is saved and the bindingsorce position is updated to the new row DataRowView drv = myForm.CurrentRow; avaliadoTableAdapter.Update(drv.Row); avaliadoBindingSource.Position = avaliadoBindingSource.Find("ID", drv.Row.ItemArray[0]); The problem is that this table has a AUTOINCREMENT field and the value saved may not correspond the the value the bindingSource gives in EDIT TIME. So, when I close and open the DataGridView again the new rowd give its ID based on the available slot in the undelying DB at the momment is was saved and it just ignores the value the BindingSource generated ad EDIT TIME, Since the value given by the binding source should be used by another table as a foreingKey it make the reference insconsistent. There's a way to get the real ID was saved to the database?

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• Can't find which row is causing conversion error

  - by Marwan

  I have the following table: CREATE TABLE [dbo].[Accounts1]( [AccountId] [nvarchar](50) NULL, [ExpiryDate] [nvarchar](50) NULL ) I am trying to convert nvarchar to datetime using this query: select convert(datetime, expirydate) from accounts I get this error: Conversion failed when converting datetime from character string. The status bar says "2390 rows". I go to rows 2390, 2391 and 2392. There is nothing wrong with the data there. I even try to convert those particular rows and it works. How can I find out which row(s) is causing the conversion error?

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• How do views reduce code duplication?

  - by Debuger

  Hi! I read something like this about db views: Views are incredibly powerful and useful for one reason that stands out above all the other very good reasons. They reduce code duplication. That is, in most cases, the bottom line. If a query will be used in three or more places, then a view will drastically simplify your changes if the schema or query parameters change. I once had to edit 22 stored procedures to change some query logic. If the original architecture had utilized views, then I would have had only three changes. Can anyone explain to me how it works, and maybe give me some examples? Best regards!

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• Struggling to create correct relationships in MS Access

  - by Yandawl

  http://img714.imageshack.us/img714/7820/croppercapture1.png Basically: an award(course) has many units, which can be either optional or core(mandatory), depending on the award. So for example: the unit 'Advanced Software Engineering' maybe a core unit for the award 'Software Engineering BSc' but only an optional unit for the course 'Web Technology BSc'. I've used flags for that purpose. A student is enrolled on an award so I need to get a complete list of core and optional units (bearing in mind that a student chooses 1 out of many possible optional units). Also, these units have events, e.g, a lecture, workshop or seminar, etc. and those events have sessions or instances of events where students enrolled on that particular unit are required to attend, and those attendances are stored in a separate table to form a register. So I need a hierarchy of expanding the tables something like this I guess: Awards - Students - Units - Sessions - Attendances Any help with this would be appreciated... It's blowing my mind and I'm really close to going insane! My tutor didn't spot I'd got it wrong when I showed my original data model to him and it's due in next week! Thank you :D

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• Odd GROUP BY output DB2 - Results not as expected

  - by CallCthulhu

  If I run the following query: select load_cyc_num , crnt_dnlq_age_cde , sum(cc_min_pymt_amt) as min_pymt , sum(ec_tot_bal) as budget , case when ec_tot_bal 0 then 'Y' else 'N' end as budget , case when ac_stat_cde in ('A0P','A1P','ARP','A3P') then 'Y' else 'N' end as arngmnt , sum(sn_close_bal) as st_bal from statements where (sn_close_bal 0 or ec_tot_bal 0) and load_cyc_num in (200911) group by load_cyc_num , crnt_dnlq_age_cde , case when ec_tot_bal 0 then 'Y' else 'N' end , case when ac_stat_cde in ('A0P','A1P','ARP','A3P') then 'Y' else 'N' end then I get the correct "BUDGET" grouping, but not the correct "ARRANGEMENT" grouping, only two rows have a "Y". If I change the order of the case statements in the GROUP BY, then I get the correct grouping (full Y-N breakdown for both columns). Am I missing something obvious?

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• same table, 1 field to 2 field query

  - by edib

  I have 2 tables: 1st holds employees (of ones in any position) and the 2nd holds manager employee relations with id numbers. I want to write a query like 1st field: name(employee), 2nd field: name(manager) How can I do that?

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• comparing data via a function

  - by tigermain

  I have two sets of data (locations) in seperate tables and I need to compare if they match or not. I have a UDF which performs a calculation based upon 5 values from each table. How do I perform a select with a join using this udf? my udf is basically defined by.... ALTER FUNCTION [dbo].[MatchRanking] ( @Latitude FLOAT , @Longitude FLOAT , @Postcode VARCHAR(16) , @CompanyName VARCHAR(256) , @TelephoneNumber VARCHAR(32) , @Latitude2 FLOAT , @Longitude2 FLOAT , @Postcode2 VARCHAR(16) , @CompanyName2 VARCHAR(256) , @TelephoneNumber2 VARCHAR(32) ) RETURNS INT

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• why shrink a sqlserver 2005 database?

  - by digiguru

  What are the advantages and disadvantages of shrinking a database? Are there any performance implications?

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• Can I serialize an object if I didn't write the class used to instantiate that object?

  - by Richard77

  Hello, I've a simple class [Serializable] public class MyClass { public String FirstName { get; set: } public String LastName { get; set: } //Bellow is what I would like to do //But, it's not working //I get an exception ContactDataContext db = new ContactDataContext(); public void Save() { Contact contact = new Contact(); contact.FirstName = FirstName; contact.LastName = LastName; db.Contacts.InsertOnSubmit(contact); db.SubmitChanges(); } } I wanted to attach a Save method to the class so that I could call it on each object. When I introduced the above statement which contains ContactDataContext, I got the following error "In assembly ... PublicKeyToken=null' is not marked as serializable" It's clear that the DataContext class is generated by the framework (). I checked and did not see where that class was marked serialize. What can I do to overcome that? What's the rule when I'm not the author of a class? Just go ahead and mark the DataContext class as serializable, and pretend that everything will work? Thanks for helping

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• Query a range of date

  - by juniorSE

  Hello Guys, Im trying to query a sort of from - to date. e.g. 20-01-2010 to 20-02-2010. this should include the mentioned dates. i've tried the following queries but none works. select * from [tableName] where date = '20-01-2010' AND date <= '20-02-2010' the date where date is equal to 20-02-2010 does not show. i don't know why. select * from [tableName] where date between '20-01-2010' AND '20-02-2010' the mentioned dates is not included in the results. i want it to be included in the results. please help. thanks in advance! :)

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• Error: The conversion of a nvarchar data type to a datetime data type resulted in an out-of-range value

  - by CPM

  I know that there are simmilar questions like this on the forum, however I am still having problems to update a datetime field o the database. I dont get any problems when inserting but I get problems when updating and I am formating the same way , like this: e.Values.Item("SelectionStartDate") = Format(startdate, "yyyy-MM-dd") + " " + startTime1 + ".000" startTime is of type string. I have tried different solution that I came across on the internet but still get this error. Please help. Thanks in advance

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• Using PHP variables inside SQL statements?

  - by Homer

  For some reason I can't pass a var inside a mysql statement. I have a function that can be used for multiple tables. So instead of repeating the code I want to change the table that is selected from like so, function show_all_records($table_name) { mysql_query("SELECT * FROM $table_name"); etc, etc... } And to call the function I use show_all_records("some_table") or show_all_records("some_other_table") depending on which table I want to select from at the moment. But it's not working, is this because variables can't be passed through mysql statements?

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• Building a subquery with ARel in Rails3

  - by Christopher

  I am trying to build this query in ARel: SELECT FLOOR(AVG(num)) FROM ( SELECT COUNT(attendees.id) AS num, meetings.club_id FROM `meetings` INNER JOIN `attendees` ON `attendees`.`meeting_id` = `meetings`.`id` WHERE (`meetings`.club_id = 1) GROUP BY meetings.id) tmp GROUP BY tmp.club_id It returns the average number of attendees per meeting, per club. (a club has many meetings and a meeting has many attendees) So far I have (declared in class Club < ActiveRecord::Base): num_attendees = meetings.select("COUNT(attendees.id) AS num").joins(:attendees).group('meetings.id') Arel::Table.new('tmp', self.class.arel_engine).from(num_attendees).project('FLOOR(AVG(num))').group('tmp.club_id').to_sql but, I am getting the error: undefined method `visit_ActiveRecord_Relation' for #<Arel::Visitors::MySQL:0x9b42180> The documentation for generating non trivial ARel queries is a bit hard to come by. I have been using http://rdoc.info/github/rails/arel/master/frames Am I approaching this incorrectly? Or am I a few methods away from a solution?

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