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  • What resources will help me understand the fundamentals of Relational Database Systems.

    - by Rachel
    This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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  • Linq2SQL vs NHibernate performance (have I gone mad?)

    - by HeavyWave
    I have written the following tests to compare performance of Linq2SQL and NHibernate and I find results to be somewhat strange. Mappings are straight forward and identical for both. Both are running against a live DB. Although I'm not deleting Campaigns in case of Linq, but that shouldn't affect performance by more than 10 ms. Linq: [Test] public void Test1000ReadsWritesToAgentStateLinqPrecompiled() { Stopwatch sw = new Stopwatch(); Stopwatch swIn = new Stopwatch(); sw.Start(); for (int i = 0; i < 1000; i++) { swIn.Reset(); swIn.Start(); ReadWriteAndDeleteAgentStateWithLinqPrecompiled(); swIn.Stop(); Console.WriteLine("Run ReadWriteAndDeleteAgentState: " + swIn.ElapsedMilliseconds + " ms"); } sw.Stop(); Console.WriteLine("Total Time: " + sw.ElapsedMilliseconds + " ms"); Console.WriteLine("Average time to execute queries: " + sw.ElapsedMilliseconds / 1000 + " ms"); } private static readonly Func<AgentDesktop3DataContext, int, EntityModel.CampaignDetail> GetCampaignById = CompiledQuery.Compile<AgentDesktop3DataContext, int, EntityModel.CampaignDetail>( (ctx, sessionId) => (from cd in ctx.CampaignDetails join a in ctx.AgentCampaigns on cd.CampaignDetailId equals a.CampaignDetailId where a.AgentStateId == sessionId select cd).FirstOrDefault()); private void ReadWriteAndDeleteAgentStateWithLinqPrecompiled() { int id = 0; using (var ctx = new AgentDesktop3DataContext()) { EntityModel.AgentState agentState = new EntityModel.AgentState(); var campaign = new EntityModel.CampaignDetail { CampaignName = "Test" }; var campaignDisposition = new EntityModel.CampaignDisposition { Code = "123" }; campaignDisposition.Description = "abc"; campaign.CampaignDispositions.Add(campaignDisposition); agentState.CallState = 3; campaign.AgentCampaigns.Add(new AgentCampaign { AgentState = agentState }); ctx.CampaignDetails.InsertOnSubmit(campaign); ctx.AgentStates.InsertOnSubmit(agentState); ctx.SubmitChanges(); id = agentState.AgentStateId; } using (var ctx = new AgentDesktop3DataContext()) { var dbAgentState = ctx.GetAgentStateById(id); Assert.IsNotNull(dbAgentState); Assert.AreEqual(dbAgentState.CallState, 3); var campaignDetails = GetCampaignById(ctx, id); Assert.AreEqual(campaignDetails.CampaignDispositions[0].Description, "abc"); } using (var ctx = new AgentDesktop3DataContext()) { ctx.DeleteSessionById(id); } } NHibernate (the loop is the same): private void ReadWriteAndDeleteAgentState() { var id = WriteAgentState().Id; StartNewTransaction(); var dbAgentState = agentStateRepository.Get(id); Assert.IsNotNull(dbAgentState); Assert.AreEqual(dbAgentState.CallState, 3); Assert.AreEqual(dbAgentState.Campaigns[0].Dispositions[0].Description, "abc"); var campaignId = dbAgentState.Campaigns[0].Id; agentStateRepository.Delete(dbAgentState); NHibernateSession.Current.Transaction.Commit(); Cleanup(campaignId); NHibernateSession.Current.BeginTransaction(); } Results: NHibernate: Total Time: 9469 ms Average time to execute 13 queries: 9 ms Linq: Total Time: 127200 ms Average time to execute 13 queries: 127 ms Linq lost by 13.5 times! Event with precompiled queries (both read queries are precompiled). This can't be right, although I expected NHibernate to be faster, this is just too big of a difference, considering mappings are identical and NHibernate actually executes more queries against the DB.

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  • Conditional Join - join 1 tables 2 ways

    - by Jon H
    I have a set of (not very well normalised or relational) tables named PLAN, GROUP, PRODUCT CLIENT Most have linkage i.e. PLAN - CLIENT on clno GROUP to PRODUCT on PRODCD However, the linkage between PLAN and GROUP is tricky. A plan has 2 field of interest GRPNO and PRODCD. What I want to do is if GRPNO != 0 then join GROUP on GRPNO. However if GRPNO = 0 then I want to join GROUP on PRODCD. The frustrating thing is that the fileds I want to return in my queries are the same across the board I just need to be able to vary the join, or join the same table twice. The best I can come up with is 2 queries and merge them using datasets, or possibly using a union. Is there a nifty way to do this in one select? I should point out I am access Foxpro over ODBC to do this. Thank you!

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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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  • SQLite long to wide formats?

    - by Stephen
    Hi, I wonder if there is a canonical way to convert data from long to wide format in SQLite (is that operation usually in the domain of relational databases?). I tried to follow this example for MySQL but I guess SQLite does not have the same IF construct... Thanks!

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  • MS ACCESS: How can i count distinct value using access query?

    - by Sadat
    here is the current complex query given below. SELECT DISTINCT Evaluation.ETCode, Training.TTitle, Training.Tcomponent, Training.TImpliment_Partner, Training.TVenue, Training.TStartDate, Training.TEndDate, Evaluation.EDate, Answer.QCode, Answer.Answer, Count(Answer.Answer) AS [Count], Questions.SL, Questions.Question FROM ((Evaluation INNER JOIN Training ON Evaluation.ETCode=Training.TCode) INNER JOIN Answer ON Evaluation.ECode=Answer.ECode) INNER JOIN Questions ON Answer.QCode=Questions.QCode GROUP BY Evaluation.ETCode, Answer.QCode, Training.TTitle, Training.Tcomponent, Training.TImpliment_Partner, Training.Tvenue, Answer.Answer, Questions.Question, Training.TStartDate, Training.TEndDate, Evaluation.EDate, Questions.SL ORDER BY Answer.QCode, Answer.Answer; There is an another column Training.TCode. I need to count distinct Training.TCode, can anybody help me? If you need more information please let me know

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  • What are the disadvantages of VistaDB

    - by PhantomTypist
    I am looking into using a lightweight serverless database engine like SQLite, Firebird, or VistaDB in an upcoming project. Someone asked about What are the advantages of VistaDB. I would like to know what are the disadvantages of using VistaDB versus other technology?

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  • MySQL - Finding time overlaps

    - by Jude
    Hi, I have 2 tables in the database with the following attributes: Booking ======= booking_id booking_start booking_end resource_booked =============== booking_id resource_id The second table is an associative entity between "Booking" and "Resource" (i.e., 1 booking can contain many resources). Attributes booking_start and booking_end are timestamps with date and time in it. May I know how I might be able to find out for each resource_id (resource_booked) if the date/time overlaps or clashes with other bookings of similar resource_id? I was doodling the answer on paper, pictorially, to see if it might help me visualize how I could solve this and I got this: Joining the 2 tables (Booking, Booked_resource) into one table with the 4 attributes needed. Follow the answer suggested here : http://stackoverflow.com/questions/689458/find-overlapping-date-time-rows-within-one-table I did step 1 but step 2 is leaving me baffled! I would really appreciate any help on this! Thanks!

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  • postgresql: Fast way to update the latest inserted row

    - by Anonymous
    What is the best way to modify the latest added row without using a temporary table. E.g. the table structure is id | text | date My current approach would be an insert with the postgresql specific command "returning id" so that I can update the table afterwards with update myTable set date='2013-11-11' where id = lastRow However I have the feeling that postgresql is not simply using the last row but is iterating through millions of entries until "id = lastRow" is found. How can i directly access the last added row?

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  • How to efficiently SELECT rows from database table based on selected set of values

    - by Chau Chee Yang
    I have a transaction table of 1 million rows. The table has a field name "Code" to keep customer's ID. There are about 10,000 different customer code. I have an GUI interface allow user to render a report from transaction table. User may select arbitrary number of customers for rendering. I use IN operator first and it works for few customers: SELECT * FROM TRANS_TABLE WHERE CODE IN ('...', '...', '...') I quickly run into problem if I select few thousand customers. There is limitation using IN operator. An alternate way is create a temporary table with only one field of CODE, and inject selected customer codes into the temporary table using INSERT statement. I may then using SELECT A.* FROM TRANS_TABLE A INNER JOIN TEMP B ON (A.CODE=B.CODE) This works nice for huge selection. However, there is performance overhead for temporary table creation, INSERT injection and dropping of temporary table. Do you aware of better solution to handle this situation?

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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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  • Logical operator AND having higher order of precedence than IN

    - by AspOnMyNet
    I’ve read that logical operator AND has higher order of precedence than logical operator IN, but that doesn’t make sense since if that was true, then wouldn’t in the following statement the AND condition got evaluated before the IN condition ( thus before IN operator would be able to check whether Released field equals to any of the values specified within parentheses ? SELECT Song, Released, Rating FROM Songs WHERE Released IN (1967, 1977, 1987) AND SongName = ’WTTJ’ thanx

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  • ms-access: DB engine cannot find input table or query

    - by every_answer_gets_a_point
    here's the query: SELECT * FROM (SELECT [Occurrence Number], [Occurrence Date], [1 0 Preanalytical (Before Testing)], [Cup Type], NULL as [2 0 Analytical (Testing Phase)], [2 0 Area], NULL as [3 0 Postanalytical ( After Testing)],NULL as [4 0 Other], [Practice Code], [Specimen ID #] FROM [Lab Occurrence Form] WHERE NOT ([1 0 Preanalytical (Before Testing)] IS NULL) UNION SELECT [Occurrence Number], [Occurrence Date],NULL, [Cup Type],[2 0 Analytical (Testing Phase)], [2 0 Area], NULL,NULL, [Practice Code], [Specimen ID #] FROM [Lab Occurrence Form] WHERE NOT ([2 0 Analytical (Testing Phase)] IS NULL) UNION SELECT [Occurrence Number], [Occurrence Date],NULL, [Cup Type],NULL, [2 0 Area], [3 0 Postanalytical ( After Testing)],NULL, [Practice Code], [Specimen ID #] FROM [Lab Occurrence Form] WHERE NOT ([3 0 Postanalytical ( After Testing)] IS NULL) UNION SELECT [Occurrence Number], [Occurrence Date],NULL, [Cup Type],NULL, [2 0 Area], NULL, [4 0 Other] FROM [Lab Occurrence Form], [Practice Code], [Specimen ID #] WHERE NOT ([4 0 Other] IS NULL) ) AS mySubQuery ORDER BY mySubQuery.[Occurrence Number]; for some reason it doesnt like [Practice Code]. it's definitely a column in the table so i dont understand the problem. the error is the microsoft office access database engine cannot find the input table or query 'Practice Code'........

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  • Problem with nested lambda expressions.

    - by Lehto
    Hey I'm trying to do a nested lambda expression like to following: textLocalizationTable.Where( z => z.SpokenLanguage.Any( x => x.FromCulture == "en-GB") ).ToList(); but i get the error: Member access 'System.String FromCulture' of 'DomainModel.Entities.SpokenLanguage' not legal on type 'System.Data.Linq.EntitySet`1[DomainModel.Entities.SpokenLanguage]. TextLocalization has this relation to spokenlanguage: [Association(OtherKey = "LocalizationID", ThisKey = "LocalizationID", Storage = "_SpokenLanguage")] private EntitySet<SpokenLanguage> _SpokenLanguage = new EntitySet<SpokenLanguage>(); public EntitySet<SpokenLanguage> SpokenLanguage { set { _SpokenLanguage = value; } get { return _SpokenLanguage; } } Any idea what is wrong?

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  • Why does this query only select a single row?

    - by Joe
    SELECT * FROM tbl_houses WHERE (SELECT HousesList FROM tbl_lists WHERE tbl_lists.ID = '123') LIKE CONCAT('% ', tbl_houses.ID, '#') It only selects the row from tbl_houses of the last occuring tbl_houses.ID inside tbl_lists.HousesList I need it to select all the rows where any ID from tbl_houses exists within tbl_lists.HousesList

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  • ibatis/Oracle - SELECT query inside INSERT is failing

    - by whoopy_whale
    Hi, I'm trying to do an Insert operation using iBatis. INSERT INTO SCHEMA.TABLE (FIELD1, FIELD2, FIELD3) VALUES (#field1#, (SELECT ANOTHER_FIELD FROM SCHEMA.TABLE WHERE FIELD4= #field2#), #field2#) The inner select query always fails and returns NULL. But if I substitute #field2# with the actual value only in the inner query, it works fine. Why is iBatis not substituting fieldvalues in the innerqueries? Any ideas?

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  • Is the RESTORE process dependent on schema?

    - by Martin Aatmaa
    Let's say I have two database instances: InstanceA - Production server InstanceB - Test server My workflow is to deploy new schema changes to InstanceB first, test them, and then deploy them to InstanceA. So, at any one time, the instance schema relationship looks like this: InstanceA - Schema Version 1.5 InstanceB - Schema Version 1.6 (new version being tested) An additional part of my workflow is to keep the data in InstanceB as fresh as possible. To fulfill this, I am taking the database backups of InstanceA and applying them (restoring them) to InstanceB. My question is, how does schema version affect the restoral process? I know I can do this: Backup InstanceA - Schema Version 1.5 Restore to InstanceB - Schema Version 1.5 But can I do this? Backup InstanceA - Schema Version 1.5 Restore to InstanceB - Schema Version 1.6 (new version being tested) If no, what would the failure look like? If yes, would the type of schema change matter? For example, if Schema Version 1.6 differed from Schema Version 1.5 by just having an altered storec proc, I imagine that this type of schema change should't affect the restoral process. On the other hand, if Schema Version 1.6 differed from Schema Version 1.5 by having a different table definition (say, an additional column), I image this would affect the restoral process. I hope I've made this clear enough. Thanks in advance for any input!

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  • SQL2008 merge replication fails to update depdendent items when table is added

    - by Dan Puzey
    Setup: an existing SQL2008 merge replication scenario. A large server database, including views and stored procs, being replicated to client machines. What I'm doing: * adding a new table to the database * mark the new table for replication (using SP_AddMergeArticle) * alter a view (which is already part of the replicated content) is updated to include fields from this new table (which is joined to the tables in the existing view). A stored procedure is similarly updated. The problem: the table gets replicated to client machines, but the view is not updated. The stored procedure is also not updated. Non-useful workaround: if I run the snapshot agent after calling SP_AddMergeArticle and before updating the view/SP, both the view and the stored procedure changes correctly replicate to the client. The bigger problem: I'm running a list of database scripts in a transaction, as part of a larger process. The snapshot agent can't be run during a transaction, and if I interrupt the transaction (e.g. by running the scripts in multiple transactions), I lose the ability to roll back the changes should something fail. Does anyone have any suggestions? It seems like I must be missing something obvious, because I don't see why the changes to the view/sproc wouldn't be replicating anyway, regardless of what's going on with the new table.

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  • Merging sql queries to get different results by date

    - by pedalpete
    I am trying to build a 'recent events' feed and can't seem to get either my query correct, or figure out how to possible merge the results from two queries to sort them by date. One table holds games/, and another table holds the actions of these games/. I am trying to get the recent events to show users 1) the actions taken on games that are publicly visible (published) 2) when a new game is created and published. So, my actions table has actionId, gameid, userid, actiontype, lastupdate My games table has gameid, startDate, createdby, published, lastupdate I currently have a query like this (simplified for easy understanding I hope). SELECT actionId, actions.gameid, userid, actiontype, actions.lastupdate FROM actions JOIN ( SELECT games.gameid, startDate, createdby, published, games.lastupdate FROM games WHERE published=1 AND lastupdate>today-2 ) publishedGames on actions.gameid=games.gameid WHERE actions.type IN (0,4,5,6,7) AND actions.lastupdate>games.lastupdate and published=1 OR games.lastupdate>today-2 AND published=1 This query is looking for actions from published games where the action took place after the game was published. That pretty much takes care of the first thing that needs to be shown. However, I also need to get the results of the SELECT games.gameid, startDate, createdby, published, games.lastupdate FROM games WHERE published=1 AND startDate>today-2 so I can include in the actions list, when a new game has been published. When I run the query as I've got it written, I get all the actionids, and their gameids, but I don't get a row which shows the gameid when it was published. I understand that it may be possible that I need to run two seperate queries, and then somehow merge the results afterword with php, but I'm completely lost on where to start with that as well.

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  • php using wamp server start up error

    - by mathirengasamy
    i try to install moodle web software...i m using wamp server and sqlserver 2005 version. i install php driver for php5.3.0 thread safe version..i just paste that php_sqlsrv_ts.dll driver file into my php ext directory...i include this line extension=php_sqlsrv_ts.dll in my php.ini file... now i restart my wampserver...i m getting this error... PHP Startup: sqlsrv: Unable to initialize module Module compiled with module API=20060613 PHP compiled with module API=20090626 These options need to match get this error also in my apache log file ADODB Error: [Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified please anybody help me..

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  • Round date to fiscal year

    - by Dave Jarvis
    The following database view rounds the date back to the closest fiscal year (April 1st): CREATE OR REPLACE VIEW FISCAL_YEAR_VW AS SELECT CASE WHEN to_number(to_char( SYSDATE, 'MM' )) < 4 THEN to_date('1-APR-'||to_char(add_months(SYSDATE, -12), 'YYYY'), 'dd-MON-yyyy') ELSE to_date('1-APR-'||to_char(SYSDATE, 'YYYY'), 'dd-MON-yyyy') END AS fiscal_year FROM dual; This allows us to calculate the current fiscal year based on today's date. How can this calculation be simplified or optimized?

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  • MySQL Stored Procedures not working with SELECT (basic question)

    - by TMG
    Hello, I am using a platform (perfectforms) that requires me to use stored procedures for most of my queries, and having never used stored procedures, I can't figure out what I'm doing wrong. The following statement executes without error: DELIMITER // DROP PROCEDURE IF EXISTS test_db.test_proc// CREATE PROCEDURE test_db.test_proc() SELECT 'foo'; // DELIMITER ; But when I try to call it using: CALL test_proc(); I get the following error: #1312 - PROCEDURE test_db.test_proc can't return a result set in the given context I am executing these statements from within phpmyadmin 3.2.4, PHP Version 5.2.12 and the mysql server version is 5.0.89-community. When I write a stored procedure that returns a parameter, and then select it, things work fine (e.g.): DELIMITER // DROP PROCEDURE IF EXISTS test_db.get_sum// CREATE PROCEDURE test_db.get_sum(out total int) BEGIN SELECT SUM(field1) INTO total FROM test_db.test_table; END // DELIMITER ; works fine, and when I call it: CALL get_sum(@t); SELECT @t; I get the sum no problem. Ultimately, what I need to do is have a fancy SELECT statement wrapped up in a stored procedure, so I can call it, and return multiple rows of multiple fields. For now I'm just trying to get any select working. Any help is greatly appreciated.

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