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• Using multiple Qt (SQL) Models

  - by radix07

  I have a near real-time application that I am using Qt and an SQLite database to run. I am curious if it is safe to have two separate models access a database at once. I know 2 separate views can access a model just fine, but I can't find any document addressing this. I also realize that SQLite is thread safe for reading, so I don't see a real issue to doing this from the SQLite part of things... Basically I want to use a QSqlTableModel to do the real-time read and write in the background and at the same time use a QSqlQueryModel to give the user desired data. Since I may be doing lots of filtering in the background using the table model I can't use it as the main view as well. I have gotten this to work for the most part, but am not sure if this is the best way to do this. If the models act like multiple SQL queries I don't believe this should be an issue, but I would like to know from someone I bit more knowledgeable about this stuff since this is pretty new to me. Thanks

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• MySQL query problem

  - by Luke

  Ok, I have the following problem. I have two InnoDB tables: 'places' and 'events'. One place can have many events, but event can be created without entering place. In this case event's foreign key is NULL. Simplified structure of the tables looks as follows: CREATE TABLE IF NOT EXISTS `events` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) COLLATE utf8_bin NOT NULL, `places_id` int(9) unsigned DEFAULT NULL, PRIMARY KEY (`id`), KEY `fk_events_places` (`places_id`), ) ENGINE=InnoDB; ALTER TABLE `events` ADD CONSTRAINT `events_ibfk_1` FOREIGN KEY (`places_id`) REFERENCES `places` (`id`) ON DELETE CASCADE ON UPDATE NO ACTION; CREATE TABLE IF NOT EXISTS `places` ( `id` int(9) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) COLLATE utf8_bin NOT NULL, PRIMARY KEY (`id`), ) ENGINE=InnoDB; Question is, how to construct query which contains name of the event and name of the corresponding place (or no value, in case there is no place assigned?). I am able to do it with two queries, but then I am visibly separating events which have place assigned from the ones that are without place. Help really appreciated.

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• Logic in the db for maintaining a points system relationship?

  - by MarcusBooster

  I'm making a little web based game and need to determine where to put logic that checks the integrity of some underlying data in the sql database. Each user keeps track of points assigned to him, and points are awarded by various tasks. I keep a record of each task transaction to make sure they're not repeated, and to keep track of the value of the task at the time of completion, since an individual award level my fluctuate over time. My schema looks like this so far: create table player ( player_ID serial primary key, player_Points int not null default 0 ); create table task ( task_ID serial primary key, task_PointsAwarded int not null ); create table task_list ( player_ID int references player(player_ID), task_ID int references task(task_ID), when_completed timestamp default current_timestamp, point_value int not null, --not fk because task value may change later constraint pk_player_task_id primary key (player_ID, task_ID) ); So, the player.player_Points should be the total of all his cumulative task points in the task_list. Now where do I put the logic to enforce this? Should I do away with player.player_Points altogether and do queries every time I want to know the total score? Which seems wasteful since I'll be doing that query a lot over the course of a game. Or, put a trigger in the task_list that automatically updates the player.player_Points? Is that too much logic to have in the database and should just maintain this relationship in the application? Thanks.

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• How to update MySQL table with a cumulative count of events with the same date

  - by John

  I have a table which I pull data from. This data has a date and a stock symbol. There can be multiple rows of data with the same date and different stock symbols. I need to update the table so that there is a running total for all rows with the same date. When a new date occurs the cumulative count re-sets to 1 and then resumes. A typical query: mysql> SELECT Sym 'sym' , fdate as 'FilledDate', TsTradeNum 'numT' -> FROM trades_entered_b2 -> WHERE fDate >= '2009-08-03' AND fDate <= '2009-08-07' -> LIMIT 10; +------+------------+------+ | sym | FilledDate | numT | +------+------------+------+ | WAT | 2009-08-03 | 0 | | ALGN | 2009-08-04 | 0 | | POT | 2009-08-05 | 0 | | PTR | 2009-08-06 | 0 | | SCHW | 2009-08-06 | 0 | | FDO | 2009-08-07 | 0 | | NBL | 2009-08-07 | 0 | | RRC | 2009-08-07 | 0 | | WAT | 2009-08-08 | 0 | | COCO | 2009-08-08 | 0 | +------+------------+------+ What I want: +------+------------+------+ | sym | FilledDate | numT | +------+------------+------+ | WAT | 2009-08-03 | 1 | | ALGN | 2009-08-04 | 1 | | POT | 2009-08-05 | 1 | | PTR | 2009-08-06 | 1 | | SCHW | 2009-08-06 | 2 | | FDO | 2009-08-07 | 3 | | NBL | 2009-08-07 | 4 | | RRC | 2009-08-07 | 5 | | WAT | 2009-08-08 | 1 | | COCO | 2009-08-08 | 2 | +------+------------+------+ What I need to do is update the TsTradeNum column with the correct values. I have tried to create a function and various queries all failed. Any ideas? Thanks in advance

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• Alternative to Altova's MissionKit

  - by nomad311

  Anyone know of any good alternatives (other than those listed below which really are only good at specific XML development tasks)? The Why (if you're interested): I've been doing XML development on and off for years now, but someone brought XMLSpy to my attention recently, and it is awesome - the price isn't. Lately I've been using a combination of: Notepad++ (modifying XML) EditX (validating/debugging XML) Eclipse (designing schemas) and MS Visual Studio (validating schemas) ...based on which makes the task(s) easiest. But, I've just found out that we will be using XSL transformations to generate XML in the future. I've never used mission kit before, but I'm just short of positive XMLSpy replaces all the above mentioned tool for XML development. And if their XSL tools are anywhere near the caliber of XMLSpy ...simply put I need it. I don't believe that I can convince the budgeting types to buy licenses for MissionKit at $1000 each (won't stop me from trying). In the mean while some research on alternatives won't hurt, but a few Google queries has only revealed that not many people pay for Altova's (overpriced?) software as there are mostly links to P2P sites for downloading a more free-like version of MissionKit.

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• Return the Column Name for row with last non-null value "Ms Access 2007"

  - by bri1969

  I have a Table, which contains a list of league players. Each season, we record their Points per Dart. Their total PPD for that season is stored in other tables and extracted through other queries, which in turn are imported to the master table "Player History" at the end of the season for use as historical data. The current query retrieves each players PPD for each season they played, when they played last, and how many seasons played. The code for Last season Played has become too long and unstable to use. it was originally created, and split into two separate columns because a single SQL was to long. (LSP1) and LSP2) which work, but as I add seasons, Access does not like the length of code. In short, i need to find a more simple code that will look at each row, and look in that row for the last non null cell and report which column that last non null value is in. So if a player played seasons 30 & 31, but did not play 32..but did play 33, the Column with the code should be titled Last Season Played, and for that Player, it would state "33" in that cell, indicating that this player last played season "33" I will provide both tables and the query.. Please help

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• Question about architecting asp.net mvc application ?

  - by Misnomer

  I have read little bit about architecture and also patterns in order to follow the best practices. So this is the architecture we have and I wanted to know what you think of it and any proposed changes or improvements to it - Presentation Layer - Contains all the views,controllers and any helper classes that the view requires also it containes the reference to Model Layer and Business Layer. Business Project - Contains all the business logic and validation and security helper classes that are being used by it. It contains a reference to DataAccess Layer and Model Layer. Data Access Layer - Contains the actual queries being made on the entity classes(CRUD) operations on the entity classes. It contains reference to Model Layer. Model Layer - Contains the entity framework model,DTOs,Enums.Does not really have a reference to any of the above layers. What are your thoughts on the above architecture ? The problem is that I am getting confused by reading about like say the repository pattern, domain driven design and other design patterns. The architecture we have although not that strict still is relatively alright I think and does not really muddle things but I maybe wrong. I would appreciate any help or suggestions here. Thanks !

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• Django: getting the list of related records for a list of objects

  - by Silver Light

  Hello! I have two models related one-to many: class Person(models.Model): name = models.CharField(max_length=255); surname = models.CharField(max_length=255); age = models.IntegerField(); class Dog(models.Model): name = models.CharField(max_length=255); owner = models.ForeignKey('Person'); I want to output a list of persons below each person a list of dogs he has. Here's how I can do it: in view: persons = Person.objects.all()[0:100]; in template: {% for p in persons %} {{ p.name }} has dogs:<br /> {% for d in persons.dog_set.all %} - {{ d.name }}<br /> {% endfor %} {% endfor %} But if I do it like that, Django will execute 101 SQL queries which is very inefficient. I tried to make a custom manager, which will get all the persons, then all the dogs and links them in python, but then I can't use paginator (my another question: http://stackoverflow.com/questions/2532475/django-paginator-raw-sql-query ) and it looks quite ugly. Is there a more graceful way doing this?

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• Finding the unique paths through a Neo4j graph

  - by Larry

  I have a Neo4j graph with 12 inputs and 4 outputs, and am trying to write a query with the Java Traverser that will return the 14 unique paths from an input to an output node. All the queries I have tried return only a subset of the 14 paths. For example, the code below returns 4 paths, but the other 10 all stop 1 node short of the output. RelationshipType relType = RelationshipTypes.EDGE; TraversalDescription td = new TraversalDescriptionImpl() .depthFirst() .relationships(relType, Direction.OUTGOING); for (Node node : inputs){ Traverser tv = td.traverse(node); Iterator<Path> iter = tv.iterator(); // ... print path } I've tried uniqueness and depth settings as well, with no effect. The query below returns all 14 paths using the web interface, but when I use the ExecutionEngine class, I only get 13 paths back. START s=node(*) MATCH (s)-[p:EDGE*]->(c) WHERE s.type! = "INPUT" AND c.type! = "OUTPUT" RETURN p How do I get all the unique paths using the Java API?

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• Using the JPA Criteria API, can you do a fetch join that results in only one join?

  - by Shaun

  Using JPA 2.0. It seems that by default (no explicit fetch), @OneToOne(fetch = FetchType.EAGER) fields are fetched in 1 + N queries, where N is the number of results containing an Entity that defines the relationship to a distinct related entity. Using the Criteria API, I might try to avoid that as follows: CriteriaBuilder builder = entityManager.getCriteriaBuilder(); CriteriaQuery<MyEntity> query = builder.createQuery(MyEntity.class); Root<MyEntity> root = query.from(MyEntity.class); Join<MyEntity, RelatedEntity> join = root.join("relatedEntity"); root.fetch("relatedEntity"); query.select(root).where(builder.equals(join.get("id"), 3)); The above should ideally be equivalent to the following: SELECT m FROM MyEntity m JOIN FETCH myEntity.relatedEntity r WHERE r.id = 3 However, the criteria query results in the root table needlessly being joined to the related entity table twice; once for the fetch, and once for the where predicate. The resulting SQL looks something like this: SELECT myentity.id, myentity.attribute, relatedentity2.id, relatedentity2.attribute FROM my_entity myentity INNER JOIN related_entity relatedentity1 ON myentity.related_id = relatedentity1.id INNER JOIN related_entity relatedentity2 ON myentity.related_id = relatedentity2.id WHERE relatedentity1.id = 3 Alas, if I only do the fetch, then I don't have an expression to use in the where clause. Am I missing something, or is this a limitation of the Criteria API? If it's the latter, is this being remedied in JPA 2.1 or are there any vendor-specific enhancements? Otherwise, it seems better to just give up compile-time type checking (I realize my example doesn't use the metamodel) and use dynamic JPQL TypedQueries.

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• SYN receives RST,ACK very frequently

  - by user1289508

  Hi Socket Programming experts, I am writing a proxy server on Linux for SQL Database server running on Windows. The proxy is coded using bsd sockets and in C, and it is working just fine. When I use a database client (written in JAVA, and running on a Linux box) to fire queries (with a concurrency of 100 or more) directly to the Database server, not experiencing connection resets. But through my proxy I am experiencing many connection resets. Digging deeper I came to know that connection from 'DB client' to 'Proxy' always succeeds but when the 'Proxy' tries to connect to the DB server the connection fails, due to the SYN packet getting RST,ACK. That was to give some background. The question is : Why does sometimes SYN receives RST,ACK? 'DB client(linux)' to 'Server(windows)' ---- Works fine 'DB client(linux) to 'Proxy(Linux)' to 'Server(windows)' ----- problematic I am aware that this can happen in "connection refused" case but this definitely is not that one. SYN flooding might be another scenario, but that does not explain fine behavior while firing to Server directly. I am suspecting some socket option setting may be required, that the client does before connecting and my proxy does not. Please put some light on this. Any help (links or pointers) is most appreciated. Additional info: Wrote a C client that does concurrent connections, which takes concurrency as an argument. Here are my observations: - At 5000 concurrency and above, some connects failed with 'connection refused'. - Below 2000, it works fine. But the actual problem is observed even at a concurrency of 100 or more. Note: The problem is time dependent sometimes it never comes at all and sometimes it is very frequent and DB client (directly to server) works fine at all times .

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• mysql - multiple where and search

  - by Shamil

  I'm trying to write a SQL query that satisfies multiple criteria. Of these, most are connected via a column, so joins are possible, however, some queries are such that I'd have to search additional tables for the information. What would be the least expensive and best way to do this? Let's say that we have a few tables. One table contains information such as sales information for a server: the salesperson, client id, service lease term, timestamps etc. It is possible that a client has multiple sales but with a different "service". I'd need to pick up all of the different ones. Another table has the quotes for the services, I'd need to pick some information out about this, whilst another, which could be joined to this one has some more information. Those tables are linked by a common client ID, so joins are possible, but I'd also need to search the first table for multiple instances of the client ID. Of course, I'd want to restrict the search to certain timestamps, which I can easily do as the timestamps are stored in MySQL format.

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• Union and order by

  - by David Lively

  Consider a table like tbl_ranks -------------------------------- family_id | item_id | view_count -------------------------------- 1 10 101 1 11 112 1 13 109 2 21 101 2 22 112 2 23 109 3 30 101 3 31 112 3 33 109 4 40 101 4 51 112 4 63 109 5 80 101 5 81 112 5 88 109 I need to generate a result set with the top two(2) rows for a subset of family ids (say, 1,2,3 and 4) ordered by view count. I'd like to do something like select top 2 * from tbl_ranks where family_id = 1 order by view_count union all select top 2 * from tbl_ranks where family_id = 2 order by view_count union all select top 2 * from tbl_ranks where family_id = 3 order by view_count union all select top 2 * from tbl_ranks where family_id = 4 order by view_count but, of course, order by isn't valid in a union all context in this manner. Any suggestions? I know I could run a set of 4 queries, store the results into a temp table and select the contents of that temp as the final result, but I'd rather avoid using a temp table if possible. Note: in the real app, the number of records per family id is indeterminate, and the view_counts are also not fixed as they appear in the above example.

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• Silverlight 4 caching issue?

  - by DavidS

  I am currently experiencing a weird caching problem it would seem. When I load my data intially, I return all the data within given dates and my graph looks as follows: Then I filter the data to return a subset of the original data for the same date range (not that it matters) and I get the following view of my data: However, I intermittently get the following when I refresh the same filterd view of the data: One can see that not all the data gets cached but only some of it i.e. for 12 Dec 2010 and 5 dec 2010(not shown here). I've looked at my queries and the correct data is getting pulled out. It is only on the presentation layer i.e. on Mainpage.xaml.cs that this erroneous data seems to exist. I've stepped through the code and the data is corect through all the layers except on the presentation layer. Has anyone experienced this before? Is there some sort of caching going in the background that is keeping that data in the background as I've got browser caching off? I am using the LoadOperation in the callback method within the Load method of the DomainContext if that helps...

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• sqlobject: No connection has been defined for this thread or process

  - by Claudiu

  I'm using sqlobject in Python. I connect to the database with conn = connectionForURI(connStr) conn.makeConnection() This succeeds, and I can do queries on the connection: g_conn = conn.getConnection() cur = g_conn.cursor() cur.execute(query) res = cur.fetchall() This works as intended. However, I also defined some classes, e.g: class User(SQLObject): class sqlmeta: table = "gui_user" username = StringCol(length=16, alternateID=True) password = StringCol(length=16) balance = FloatCol(default=0) When I try to do a query using the class: User.selectBy(username="foo") I get an exception: ... File "c:\python25\lib\site-packages\SQLObject-0.12.4-py2.5.egg\sqlobject\main.py", line 1371, in selectBy conn = connection or cls._connection File "c:\python25\lib\site-packages\SQLObject-0.12.4-py2.5.egg\sqlobject\dbconnection.py", line 837, in __get__ return self.getConnection() File "c:\python25\lib\site-packages\SQLObject-0.12.4-py2.5.egg\sqlobject\dbconnection.py", line 850, in getConnection "No connection has been defined for this thread " AttributeError: No connection has been defined for this thread or process How do I define a connection for a thread? I just realized I can pass in a connection keyword which I can give conn to to make it work, but how do I get it to work if I weren't to do that?

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• Xpath query to select node when attribute does not exist? [closed]

  - by Antoine

  I want to select nodes for which a specific attribute does not exist. I've tried the Not() function, but it doesn't work. Is there a way for this? Example: The following Xpath query: group/msg[not(@owner)] Should retrieve the first node but not the 2nd one. However, both SketchPath (tool to test Xpath queries) and my C# code consider that the 2 nodes are ok. <group> <msg id="EVENTDATA_CCFLOADED_XMLCONTEXT" numericId="14026" translate="False" topicId="302" status="translated" > <text>Context</text> <comment></comment> </msg> <msg id="EVENTDATA_CCFLOADED_XMLCONTEXT_HELP" numericId="14027" translate="False" topicId="302" status="translated" owner="EVENTDATA_CCFLOADED_XMLCONTEXT" > <text>Provides the new data displayed in the Object.</text> <comment></comment> </msg> </group> In fact the Not() function works correctly, it's just that I had other conditions and parentheses weren't set correctly. errare humanum est.

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• Why is it possible to enumerate a LinqToSql query after calling Dispose() on the DataContext?

  - by DanM

  I'm using the Repository Pattern with some LinqToSql objects. My repository objects all implement IDisposable, and the Dispose() method does only thing--calls Dispose() on the DataContext. Whenever I use a repository, I wrap it in a using person, like this: public IEnumerable<Person> SelectPersons() { using (var repository = _repositorySource.GetNew<Person>(dc => dc.Person)) { return repository.GetAll(); } } This method returns an IEnumerable<Person>, so if my understanding is correct, no querying of the database actually takes place until Enumerable<Person> is traversed (e.g., by converting it to a list or array or by using it in a foreach loop), as in this example: var persons = gateway.SelectPersons(); // Dispose() is fired here var personViewModels = ( from b in persons select new PersonViewModel { Id = b.Id, Name = b.Name, Age = b.Age, OrdersCount = b.Order.Count() }).ToList(); // executes queries In this example, Dispose() gets called immediately after setting persons, which is an IEnumerable<Person>, and that's the only time it gets called. So, a couple questions: How does this work? How can a disposed DataContext still query the database for results when I walk the IEnumerable<Person>? What does Dispose() actually do? I've heard that it is not necessary (e.g., see this question) to dispose of a DataContext, but my impression was that it's not a bad idea. Is there any reason not to dispose of it?

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• LinqtoSql Pre-compile Query problem with Count() on a group by

  - by Joe Pitz

  Have a LinqtoSql query that I now want to precompile. var unorderedc = from insp in sq.Inspections where insp.TestTimeStamp > dStartTime && insp.TestTimeStamp < dEndTime && insp.Model == "EP" && insp.TestResults != "P" group insp by new { insp.TestResults, insp.FailStep } into grp select new { FailedCount = (grp.Key.TestResults == "F" ? grp.Count() : 0), CancelCount = (grp.Key.TestResults == "C" ? grp.Count() : 0), grp.Key.TestResults, grp.Key.FailStep, PercentFailed = Convert.ToDecimal(1.0 * grp.Count() / tcount * 100) }; I have created this delegate: public static readonly Funct<SQLDataDataContext, int, string, string, DateTime, DateTime, IQueryable<CalcFailedTestResult>> GetInspData = CompiledQuery.Compile((SQLDataDataContext sq, int tcount, string strModel, string strTest, DateTime dStartTime, DateTime dEndTime, IQueryable<CalcFailedTestResult> CalcFailed) => from insp in sq.Inspections where insp.TestTimeStamp > dStartTime && insp.TestTimeStamp < dEndTime && insp.Model == strModel && insp.TestResults != strTest group insp by new { insp.TestResults, insp.FailStep } into grp select new { FailedCount = (grp.Key.TestResults == "F" ? grp.Count() : 0), CancelCount = (grp.Key.TestResults == "C" ? grp.Count() : 0), grp.Key.TestResults, grp.Key.FailStep, PercentFailed = Convert.ToDecimal(1.0 * grp.Count() / tcount * 100) }); The syntax error is on the CompileQuery.Compile() statement It appears to be related to the use of the select new {} syntax. In other pre-compiled queries I have written I have had to just use the select projection by it self. In this case I need to perform the grp.count() and the immediate if logic. I have searched SO and other references but cannot find the answer.

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• Get notified when UITableView has finished asking for data?

  - by kennethmac2000

  Hi everyone, Is there some way to find out when a UITableView has finished asking for data from its data source? None of the viewDidLoad/viewWillAppear/viewDidAppear methods of the associated view controller (UITableViewController) are of use here, as they all fire too early. None of them (entirely understandably) guarantee that queries to the data source have finished for the time being (eg, until the view is scrolled). One workaround I have found is to call reloadData in viewDidAppear, since, when reloadData returns, the table view is guaranteed to have finished querying the data source as much as it needs to for the time being. However, this seems rather nasty, as I assume it is causing the data source to be asked for the same information twice (once automatically, and once because of the reloadData call) when it is first loaded. The reason I want to do this at all is that I want to preserve the scroll position of the UITableView - but right down to the pixel level, not just to the nearest row. When restoring the scroll position (using scrollRectToVisible:animated:), I need the table view to already have sufficient data in it, or else the scrollRectToVisible:animated: method call does nothing (which is what happens if you place the call on its own in any of viewDidLoad, viewWillAppear or viewDidAppear). Thanks in advance for your assistance!

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• How can I integrate advanced computations into a database field?

  - by ciclistadan

  My biological research involves the measurement of a cellular structure as it changes length throughout the course of observation (capturing images every minute for several hours). As my data sets have become larger I am trying to store them in an Access database, from which I would like to perform various queries about their changes in size. I know that the SELECT statement can incorporate some mathematical permutations, but I have been unable to incorporate many of my necessary calculations (probably due to my lack of knowledge). For example, one calculation involves determining the rate of change during specifically defined periods of growth. This calculation is entirely dependent on the raw data saved in the table, therefore I didn't this it would be appropriate to just calculate it in excel prior to entry into the field. So my question is, what would be the most appropriate method of performing this calculation. Should I attempt to string together a huge SELECT calculation in my QUERY, or is there a way to use another language (I know perl?) which can be called to populate the new query field? I'm not looking for someone to write the code, just where is it appropriate to incorporate each step. Also, I am currently using Office Access but would be interested in any mySQL answers as I may be moving to this platform at a later date. Thanks all!

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• I have data about deadlocks, but I can't understand why they occur (MS SQL/ASP.NET MVC)

  - by Alex

  I am receiving a lot of deadlocks in my big web application. http://stackoverflow.com/questions/2941233/how-to-automatically-re-run-deadlocked-transaction-asp-net-mvc-sql-server Here I wanted to re-run deadlocked transactions, but I was told to get rid of the deadlocks - it's much better, than trying to catch the deadlocks. So I spent the whole day with SQL profiler, setting the tracing keys etc. And this is what I got. There's a Users table. I have a very high usable page with the following query (it's not the only query, but it's the one that causes troubles) UPDATE Users SET views = views + 1 WHERE ID IN (SELECT AuthorID FROM Articles WHERE ArticleID = @ArticleID) And then there's the following query in ALL pages: User = DB.Users.SingleOrDefault(u => u.Password == password && u.Name == username); That's where I get User from cookies. Very often a deadlock occurs and this second LINQ TO SQL query is chosen as a victim, so it's not run, and users of my site see an error screen. I read a lot about deadlocks... And I don't understand why this is causing a deadlock. So obviously both of this queries run very often. At least once a second. Maybe even more often (300-400 users online). So they can be run at the same time very easily, but why does it cause a deadlock? Please help. Thank you

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• Speed up csv export when using php from mysql database query

  - by John

  Ok, so i've got a web system (built on codeigniter & running on mysql) that allows people to query a database of postal address data by making selections in a series of forms until they arrive at the selection that want, pretty standard stuff. They can then buy that information and download it via that system. The queries run very fast, but when it comes to applying that query to the database,and exporting it to csv, once the datasets get to around the 30,000 record mark (each row has around 40 columns of which about 20 are all populated with on average 20 chars of data per cell) it can take 5 or so minutes to export to csv. So, my question is, what is the main cause for the slowness? Is it that the resultset of data from the query is so large, that it is running into memory issues? Therefore should i allow much more memory to the process? Or, is there a much more efficient way of exporting to csv from a mysql query that i'm not doing? Should i save the contents of the query to a temp table and simply export the temp table to csv? Or am i going about this all wrong? Also, is the fact that i'm using Codeigniters Active Record for this prohibitive due to the way that it stores the resultset? Any advice is welcome! Thank you for reading!

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• MYSQL variables - SET @var

  - by Lizard

  I am attempting to create a mysql snippet that will analyse a table and remove duplicate entries (duplicates are based on two fields not entire record) I have the following code that works when I hard code the variables in the queries, but when I take them out and put them as variables I get mysql errors, below is the script SET @tblname = 'mytable'; SET @fieldname = 'myfield'; SET @concat1 = 'checkfield1'; SET @concat2 = 'checkfield2'; ALTER TABLE @tblname ADD `tmpcheck` VARCHAR( 255 ) NOT NULL; UPDATE @tblname SET `tmpcheck` = CONCAT(@concat1,'-',@concat2); CREATE TEMPORARY TABLE `tmp_table` ( `tmpfield` VARCHAR( 100 ) NOT NULL ) ENGINE = MYISAM ; INSERT INTO `tmp_table` (`tmpfield`) SELECT @fieldname FROM @tblname GROUP BY `tmpcheck` HAVING ( COUNT(`tmpcheck`) > 1 ); DELETE FROM @tblname WHERE @fieldname IN (SELECT `tmpfield` FROM `tmp_table`); ALTER TABLE @tblname DROP `tmpcheck`; I am getting the following error: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '@tblname ADD `tmpcheck` VARCHAR( 255 ) NOT NULL' at line 1 Is this because I can't use a variable for a table name? What else could be wrong or how wopuld I get around this issue. Thanks in adavnce

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• SDL (And Others) Virtual Key Input

  - by David C

  Today I set up the input in my application for all the different keys. This works fine except for virtual keys, for example, caret or ampersand. Keys that normally need shift to be got at. Using SDL these virtual keys don't work. As in they do not register an event. if (event.type == SDL_KEYDOWN) { switch (event.key.keysym.sym) { case SDLK_CARET: Keys[KeyCodes::Caret] = KeyState::Down; break; case SDLK_UP: Keys[KeyCodes::Up] = KeyState::Down; break; default: break; } I am absolutely sure my system works with physical keys like Up. The program queries a keystate like so: if (Keys[KeyCode] == KeyState::Down) { lua_pushboolean(L, true); } else { lua_pushboolean(L, false); } KeyCode is passed in as an argument. So why are virtual keys, or keys that need shift to get at not working using SDL's KeyDown event type? Is more code needed to get to them? Or am I being stupid?

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• The best way to return related data in a SQL statement

  - by Darvis Lombardo

  I have a question on the best method to get back to a piece of data that is in a related table on the other side of a many-to-many relationship table. My first method uses joins to get back to the data, but because there are multiple matching rows in the relationship table, I had to use a TOP 1 to get a single row result. My second method uses a subquery to get the data but this just doesn't feel right. So, my question is, which is the preferred method, or is there a better method? The script needed to create the test tables, insert data, and run the two queries is below. Thanks for your advice! Darvis -------------------------------------------------------------------------------------------- -- Create Tables -------------------------------------------------------------------------------------------- DECLARE @TableA TABLE ( [A_ID] [int] IDENTITY(1,1) NOT NULL, [Description] [varchar](50) NULL) DECLARE @TableB TABLE ( [B_ID] [int] IDENTITY(1,1) NOT NULL, [A_ID] [int] NOT NULL, [Description] [varchar](50) NOT NULL) DECLARE @TableC TABLE ( [C_ID] [int] IDENTITY(1,1) NOT NULL, [Description] [varchar](50) NOT NULL) DECLARE @TableB_C TABLE ( [B_ID] [int] NOT NULL, [C_ID] [int] NOT NULL) -------------------------------------------------------------------------------------------- -- Insert Test Data -------------------------------------------------------------------------------------------- INSERT INTO @TableA VALUES('A-One') INSERT INTO @TableA VALUES('A-Two') INSERT INTO @TableA VALUES('A-Three') INSERT INTO @TableB (A_ID, Description) VALUES(1,'B-One') INSERT INTO @TableB (A_ID, Description) VALUES(1,'B-Two') INSERT INTO @TableB (A_ID, Description) VALUES(1,'B-Three') INSERT INTO @TableB (A_ID, Description) VALUES(2,'B-Four') INSERT INTO @TableB (A_ID, Description) VALUES(2,'B-Five') INSERT INTO @TableB (A_ID, Description) VALUES(3,'B-Six') INSERT INTO @TableC VALUES('C-One') INSERT INTO @TableC VALUES('C-Two') INSERT INTO @TableC VALUES('C-Three') INSERT INTO @TableB_C (B_ID, C_ID) VALUES(1, 1) INSERT INTO @TableB_C (B_ID, C_ID) VALUES(2, 1) INSERT INTO @TableB_C (B_ID, C_ID) VALUES(3, 1) -------------------------------------------------------------------------------------------- -- Get result - method 1 -------------------------------------------------------------------------------------------- SELECT TOP 1 C.*, A.Description FROM @TableC C JOIN @TableB_C BC ON BC.C_ID = C.C_ID JOIN @TableB B ON B.B_ID = BC.B_ID JOIN @TableA A ON B.A_ID = A.A_ID WHERE C.C_ID = 1 -------------------------------------------------------------------------------------------- -- Get result - method 2 -------------------------------------------------------------------------------------------- SELECT C.*, (SELECT A.Description FROM @TableA A WHERE EXISTS (SELECT * FROM @TableB_C BC JOIN @TableB B ON B.B_ID = BC.B_ID WHERE BC.C_ID = C.C_ID AND B.A_ID = A.A_ID)) FROM @TableC C WHERE C.C_ID = 1

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