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  • Does AsEnumerable() cache all result (LINQ)

    - by Akshay
    When we call a query operator on a sequence, a sequence-specific operator gets called. I mean if i call Where<>() operator on IEnumerable<>, the operator that will be called will be defined in Enumerable class and if it's called on IQueryable<>, the one defined in Queryable class will be called. Consider the operator Reverse, defined in the Enumerable class. If i want to call it on Iqueryable<> then I must use the AsEnumerable<>() operator to first convert it into IEnumerable<>. db.Countries.OrderBy(cntry=>cntry.CountryName).AsEnumerable().Reverse() But the Reverse operator got to have all records at the same time so that it can reverse them. In the above code do all the records get loaded in memory first and then the Reverse() operator is reversing it ?

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  • (NOT) NULL for NVARCHAR columns

    - by Anders Abel
    Allowing NULL values on a column is normally done to allow the absense of a value to be represented. When using NVARCHAR there is aldready a possibility to have an empty string, without setting the column to NULL. In most cases I cannot see a semantical difference between an NVARCHAR with an empty string and a NULL value for such a column. Setting the column as NOT NULL saves me from having to deal with the possibility of NULL values in the code and it feels better to not have to different representations of "no value" (NULL or an empty string). Will I run into any other problems by setting my NVARCHAR columns to NOT NULL. Performance? Storage size? Anything I've overlooked on the usage of the values in the client code?

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  • MySQL: Limit output according to associated ID

    - by Jess
    So here's my situation. I have a books table and authors table. An author can have many books... In my authors page view, the user (logged in) can click an author in a tabled row and be directed to a page displaying the author's books (collected like this URI format: viewauthorbooks.php?author_id=23), very straight forward... However, in my query, I need to display the books for the author only, and not all books stored in the books table (as i currently have!) As I am a complete novice, I used the most simple query of: SELECT * FROM tasks_tb This returns the books for me, but returns every single value (book) in the database, and not ones associated with the selected author. And when I click a different author the same books are displayed for them...I think everyone gets what I'm trying to achieve, I just don't know how to perform the query. I'm guessing that I need to start using more advanced query clauses like INNER JOIN etc. Anyone care to help me out :)

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  • Migrating from mssql to firebird: pro and cons

    - by user193655
    i am considering the migration for 3 reasons: 1) SQLSERVER installation is a nightmar, expecially for 1-user software. Software installs in 10 seconds, SQLServer in 1 hour. Firebird installation is much easier. 2) SQLSERVER runs on windows server only 3) My customers have all the express edition 4) i am not using any advanced feature, I am now starting using filestream, but the main reason for this is that Express eidtion has 4/10GB db size limit So these are all Pros of moving to Firebird. Which are the cons? I can also plan to support both platiforms, but this will backfire I fear.

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  • acts-as-taggable-on: find tags with name LIKE, sort by tag_counts?

    - by James
    Hi I'm using the rails plugin acts-as-taggable-onand I'm trying to find the top 5 most used tags whose names match and partially match a given query. When I do User.skill_counts.order('count DESC').limit(5).where('name LIKE ?', params[:query]) This return the following error: ActiveRecord::StatementInvalid: SQLite3::SQLException: ambiguous column name: name: SELECT tags.*, COUNT(*) AS count FROM "tags" INNER JOIN users ON users.id = taggings.taggable_id LEFT OUTER JOIN taggings ON tags.id = taggings.tag_id AND taggings.context = 'skills' WHERE (taggings.taggable_type = 'User') AND (taggings.taggable_id IN(SELECT users.id FROM "users")) AND (name LIKE 'asd') GROUP BY tags.id, tags.name HAVING COUNT(*) > 0 ORDER BY count DESC LIMIT 5 But when I do User.skill_counts.first.name this returns "alliteration" I'd appreciate any help on this matter.

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  • How would I implement separate databases for reading and writing operations?

    - by Matt
    I am interested in implementing an architecture that has two databases one for read operations and the other for writes. I have never implemented something like this and have always built single database, highly normalised systems so I am not quite sure where to begin. I have a few parts to this question. 1. What would be a good resource to find out more about this achitecture? 2. Is it just a question of replicating between two identical schemas, or would your schemas differ depending on the operations, would normalisation vary too? 3. How do you insure that data written to one database is immediately available for reading from the second? Any further help, tips, resources would be appreciated. Thanks.

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  • How can I kill MySQL queries every 60 seconds in Windows?

    - by Ethan Allen
    I want to check my MySQL server every minute and kill queries that have run longer than 150 seconds. The main reason I want to do this is because I don't want queries from certain people to lock up the DB for everyone else. I know this is not the ultimate solution to the problem, but at least it's a fallback in case something goes wrong with a query. I don't have a slave DB (this is just an at-home project). I'd like to schedule a script to run that does this for me. I'm unfamiliar with Perl or Ruby and I need it done on my Windows 2008 Server box. I've looked into creating a simple cmd line script, but that doesn't seem to be possible. I know currently I can do something like this but I have to do it manually: mysqladmin processlist mysqladmin kill Anyone have any ideas or examples on how I could do this?

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  • Voting Script, Possibility of Simplifying Database Queries

    - by Sev
    I have a voting script which stores the post_id and the user_id in a table, to determine whether a particular user has already voted on a post and disallow them in the future. To do that, I am doing the following 3 queries. SELECT user_id, post_id from votes_table where postid=? AND user_id=? If that returns no rows, then: UPDATE post_table set votecount = votecount-1 where post_id = ? Then SELECT votecount from post where post_id=? To display the new votecount on the web page Any better way to do this? 3 queries are seriously slowing down the user's voting experience Edit In the votes table, vote_id is a primary key In the post table, post_id is a primary key. Any other suggestions to speed things up?

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  • Beginner Ques::How to delete records permanently in case of linked tables?

    - by Serenity
    Let's say I have these 2 tables QuesType and Ques:- QuesType QuestypeID|QuesType |Active ------------------------------------ 101 |QuesType1 |True 102 |QuesType2 |True 103 |XXInActiveXX |False Ques QuesID|Ques|Answer|QUesTypeID|Active ------------------------------------ 1 |Ques1|Ans1 |101 |True 2 |Ques2|Ans2 |102 |True 3 |Ques3|Ans3 |101 |True In the QuesType Table:- QuesTypeID is a Primary key In the Ques Table:- QuesID is a Primary key and QuesType ID is the Foreign Key that refernces QuesTypeID from QuesType Table Now I am unable to delete records from QuesType Table, I can only make QuesType inactive by setting Active=False. I am unable to delete QuesTypes permanently because of the Foreign key relation it has with Ques Table. So , I just set the column Active=false and those Questypes then don't show on my grid wen its binded. What I want to do is be able to delete any QuesType permamnently. Now it can only be deleted if its not being used anywhere in the Ques table, right? So to delete any QuesType permanently I thot this is what I could do:- In the grid that displays QuesTypes, I have this check box for Active and a button for delete.What I thot was, when a user makes some QuesType inactive then OnCheckChanged() event will run and that will have the code to delete all the Questions in Ques table that are using that QuesTypeID. Then on the QuesType grid, that QuesType would show as Deactivated and only then can a user delete it permanently. Am I thinking correctly? Currently in my DeleteQuesType Stored Procedure what I am doing is:- Setting the Active=false and Setting QuesTye= some string like XXInactiveXX Is there any other way?

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  • If a table has two xml columns, will inserting records be a lot slower?

    - by Lieven Cardoen
    Is it a bad thing to have two xml columns in one table? + How much slower are these xml columns in terms of updating/inserting/reading data? In profiler this kind of insert normally takes 0 ms, but sometimes it goes up to 160ms: declare @p8 xml set @p8=convert(xml,N'<interactions><interaction correct="false" score="0" id="0" gapid="0" x="61" y="225"><feedback/><element id="0" position="0" elementtype="1"><asset/></element></interaction><interaction correct="false" score="0" id="1" gapid="1" x="64" y="250"><feedback/><element id="0" position="0" elementtype="1"><asset/></element></interaction><interaction correct="false" score="0" id="2" gapid="2" x="131" y="250"><feedback/><element id="0" position="0" elementtype="1"><asset/></element></interaction></interactions>') declare @p14 xml set @p14=convert(xml,N'<contentinteractions/>') exec sp_executesql N'INSERT INTO [dbo].[PackageSessionNodes]([dbo].[PackageSessionNodes].[PackageSessionId], [dbo].[PackageSessionNodes].[TreeNodeId],[dbo].[PackageSessionNodes].[Duration], [dbo].[PackageSessionNodes].[Score],[dbo].[PackageSessionNodes].[ScoreMax], [dbo].[PackageSessionNodes].[Interactions],[dbo].[PackageSessionNodes].[BrainTeaser], [dbo].[PackageSessionNodes].[DateCreated], [dbo].[PackageSessionNodes].[CompletionStatus], [dbo].[PackageSessionNodes].[ReducedScore], [dbo].[PackageSessionNodes].[ReducedScoreMax], [dbo].[PackageSessionNodes].[ContentInteractions]) VALUES (@ins_dboPackageSessionNodesPackageSessionId, @ins_dboPackageSessionNodesTreeNodeId, @ins_dboPackageSessionNodesDuration, @ins_dboPackageSessionNodesScore, @ins_dboPackageSessionNodesScoreMax, @ins_dboPackageSessionNodesInteractions, @ins_dboPackageSessionNodesBrainTeaser, @ins_dboPackageSessionNodesDateCreated, @ins_dboPackageSessionNodesCompletionStatus, @ins_dboPackageSessionNodesReducedScore, @ins_dboPackageSessionNodesReducedScoreMax, @ins_dboPackageSessionNodesContentInteractions) ; SELECT SCOPE_IDENTITY() as new_id This is the table: CREATE TABLE [dbo].[PackageSessionNodes]( [PackageSessionNodeId] [int] IDENTITY(1,1) NOT NULL, [PackageSessionId] [int] NOT NULL, [TreeNodeId] [int] NOT NULL, [Duration] [int] NULL, [Score] [float] NOT NULL, [ScoreMax] [float] NOT NULL, [Interactions] [xml] NOT NULL, [BrainTeaser] [bit] NOT NULL, [DateCreated] [datetime] NULL, [CompletionStatus] [int] NOT NULL, [ReducedScore] [float] NOT NULL, [ReducedScoreMax] [float] NOT NULL, [ContentInteractions] [xml] NOT NULL, CONSTRAINT [PK_PackageSessionNodes] PRIMARY KEY CLUSTERED ( [PackageSessionNodeId] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] GO ALTER TABLE [dbo].[PackageSessionNodes] WITH CHECK ADD CONSTRAINT [FK_PackageSessionNodes_PackageSessions] FOREIGN KEY([PackageSessionId]) REFERENCES [dbo].[PackageSessions] ([PackageSessionId]) ON UPDATE CASCADE ON DELETE CASCADE GO ALTER TABLE [dbo].[PackageSessionNodes] CHECK CONSTRAINT [FK_PackageSessionNodes_PackageSessions] GO ALTER TABLE [dbo].[PackageSessionNodes] WITH CHECK ADD CONSTRAINT [FK_PackageSessionNodes_TreeNodes] FOREIGN KEY([TreeNodeId]) REFERENCES [dbo].[TreeNodes] ([TreeNodeId]) GO ALTER TABLE [dbo].[PackageSessionNodes] CHECK CONSTRAINT [FK_PackageSessionNodes_TreeNodes] GO ALTER TABLE [dbo].[PackageSessionNodes] ADD CONSTRAINT [DF_PackageSessionNodes_Score] DEFAULT ((-1)) FOR [Score] GO ALTER TABLE [dbo].[PackageSessionNodes] ADD CONSTRAINT [DF_PackageSessionNodes_ScoreMax] DEFAULT ((-1)) FOR [ScoreMax] GO ALTER TABLE [dbo].[PackageSessionNodes] ADD CONSTRAINT [DF_PackageSessionNodes_DateCreated] DEFAULT (getdate()) FOR [DateCreated] GO ALTER TABLE [dbo].[PackageSessionNodes] ADD CONSTRAINT [DF_PackageSessionNodes_ReducedScore] DEFAULT ((-1)) FOR [ReducedScore] GO ALTER TABLE [dbo].[PackageSessionNodes] ADD CONSTRAINT [DF_PackageSessionNodes_ReducedScoreMax] DEFAULT ((-1)) FOR [ReducedScoreMax] GO

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  • Looking for MSSQL Table Design Sanity Check for Profile Tables with Dynamic Columns.

    - by Code Sherpa
    I just want a general sanity check regarding database design. We are building a web system that has both Teachers and Students. Both have accounts in the system. Both have profiles in the system. My question is about the table design of those Profile tables. The Teacher profile is pretty static regarding the metadata associated with it. Each teacher has a set number of fields that exposes information about that individual (schools, degrees, etc). The students, however, are a different case. We are using a windows service to pull varying data about the students from an endless stream of excel spreadsheets. The data gets moved into our database and then the fields appear in association with the student's profile. Accordingly, each and every student may have very different fields in their profile. I originally started with the concept of three tables: Accounts ---------- AccountID TeacherProfiles ---------- TeacherProfileID AccountID SecondarySchool University YearsTeaching Etc... StudentProfiles ---------- StudentProfileID AccountID Header Value The StudentProfiles table would hold the name of the column headers from the excel spreadsheets and the associated values. I have since evolved the design a little to treat Profiles more generically per the attached ERD image. The Teacher and Student "Headers" are stored in a table called "ProfileAttributeTypes" and responses (either from the excel document or via input fields on the web form) are put in a ProfileAttributes table. This way both Student and Teacher profiles can be associated with a dynamic flow of profile fields. The "Permissions" table tells us whether we are dealing with a Student or a Teacher. Since this system is likely to grow quickly, I want to make sure the foundation is solid. Can you please provide feedback about this design and let me know if it seems sound or if you could see problems it might create and, if so, what might be a better approach? Thanks in advance.

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  • get records from sqlite group by month

    - by peacmaker
    hi i hve an sqlite db which contain transactions each transaction has an price and has an transDate i want to retrieve the sum of the transaction group by month so the retrieved records should be like the following Price month 230 2 500 3 400 4 pleas any help

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  • Exporting many tables on Oracle

    - by Adomas
    Hi, I would like to know, how to export many tables from oracle DB. I use exp.exe, create file expdat.dmp and so on. I choose to export only tables and there I must write which ones. Is there any chance of getting all of them? thanks

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  • ORACLE: Parameter reference in WHERE doesn't work

    - by Gainder
    Hello, I have created a simple static function in oracle 10g to get the reference of an object based on his pk. STATIC FUNCTION getRef(nome IN VARCHAR2) RETURN REF folder_typ IS fl_r REF folder_typ := null; BEGIN SELECT REF(fl) INTO fl_r FROM folder_tab fl WHERE fl.nome = nome; RETURN fl_r; END getRef; This gives me an error because it could't fetch a row. If insted of WHERE fl.nome = nome; I write WHERE fl.nome = 'folder1'; -- it works. I think im not using the parameter in the right way. How can I use it?

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  • How can i learn Table Name in database an column name?

    - by Phsika
    How can i learn table Name in database an how can i learn any Table's Column name? SELECT Col.COLUMN_NAME, Col.DATA_TYPE FROM INFORMATION_SCHEMA.COLUMNS AS Col LEFT OUTER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE AS Usg ON Col.TABLE_NAME = Usg.TABLE_NAME AND Col.COLUMN_NAME = Usg.COLUMN_NAME LEFT OUTER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS Con ON Usg.CONSTRAINT_NAME = Con.CONSTRAINT_NAME WHERE Col.TABLE_NAME = 'Addresses_Temp' AND Con.Constraint_TYPE = 'PRIMARY KEY' But it returns to me empty data:(

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  • Why can't you return a List from a Compiled Query?

    - by Andrew
    I was speeding up my app by using compiled queries for queries which were getting hit over and over. I tried to implement it like this: Function Select(ByVal fk_id As Integer) As List(SomeEntity) Using db As New DataContext() db.ObjectTrackingEnabled = False Return CompiledSelect(db, fk_id) End Using End Function Shared CompiledSelect As Func(Of DataContext, Integer, List(Of SomeEntity)) = _ CompiledQuery.Compile(Function(db As DataContext, fk_id As Integer) _ (From u In db.SomeEntities _ Where u.SomeLinkedEntity.ID = fk_id _ Select u).ToList()) This did not work and I got this error message: Type : System.ArgumentNullException, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 Message : Value cannot be null. Parameter name: value However, when I changed my compiled query to return IQueryable instead of List like so: Function Select(ByVal fk_id As Integer) As List(SomeEntity) Using db As New DataContext() db.ObjectTrackingEnabled = False Return CompiledSelect(db, fk_id).ToList() End Using End Function Shared CompiledSelect As Func(Of DataContext, Integer, IQueryable(Of SomeEntity)) = _ CompiledQuery.Compile(Function(db As DataContext, fk_id As Integer) _ From u In db.SomeEntities _ Where u.SomeLinkedEntity.ID = fk_id _ Select u) It worked fine. Can anyone shed any light as to why this is? BTW, compiled queries rock! They sped up my app by a factor of 2.

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  • Access: Expression too complex to be evaluated

    - by user2502964
    I'm trying to sort out values from a database by the weekending date. The script I'm using functions on 6 of my 7 databases (they are all constructed identically). The 7th database doesn't function. I get the expression too complex error. any help figuring out why?? Here is my code: SELECT UPC_Test.Type, UPC_Test.[Model No], UPC_Test.[Model Desc], UPC_Test.[Serial No], Format(DateValue([UPC_Test].[Test Date]+7-Weekday([UPC_Test].[Test Date],0)),"m/d/yyyy") AS [Test Date], UPC_Test.Parameter, UPC_Test.[Failure Symptom], UPC_Test.[Repair Action], UPC_Test.[Factory Select], UPC_Test.[Test Station] FROM UPC_Test GROUP BY UPC_Test.Type, UPC_Test.[Model No], UPC_Test.[Model Desc], UPC_Test.[Serial No], Format(DateValue([UPC_Test].[Test Date]+7-Weekday([UPC_Test].[Test Date],0)),"m/d/yyyy"), UPC_Test.Parameter, UPC_Test.[Failure Symptom], UPC_Test.[Repair Action], UPC_Test.[Factory Select], UPC_Test.[Test Station] HAVING (((UPC_Test.Type)="Production") AND ((Format(DateValue([UPC_Test].[Test Date]+7-Weekday([UPC_Test].[Test Date],0)),"m/d/yyyy"))=[Enter]) AND ((UPC_Test.[Failure Symptom])<>"") AND ((UPC_Test.[Repair Action])<>"") AND ((UPC_Test.[Test Station])="UPC RF Test")) ORDER BY Format(DateValue([UPC_Test].[Test Date]+7-Weekday([UPC_Test].[Test Date],0)),"m/d/yyyy");

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  • Highlight row in report?

    - by sanjeev40084
    I have a SSRS report which displays hundred of rows. I was wondering if there is anyway i can highlight the rows so that i can easily know on which row i am while accessing the report. Any thoughts?

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  • How to: Display multiple related classes in an ASP.NET GridView ?

    - by kversch
    I would like to display students and their grades with a GridView and LinqToSQL like this: assignment1 assignment2 Student 1 55 89 Student 2 87 56 Student 3 92 34 I found this topic but it doesn't answer my question: http://forums.asp.net/t/1557987.aspx I have a many-to-many relationship between students and assignments called "grades". The grade for the assignment is stored in that table in a "gradeNumber" column. I would also like to specify which assignments should be displayed in the grid. Btw, my LINQ entities are extended to allow me to write/get studentx.Assignments or assignmentx.Students.

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  • Strange behavior with large Object Types

    - by Peter Lang
    I recognized that calling a method on an Oracle Object Type takes longer when the instance gets bigger. The code below just adds rows to a collection stored in the Object Type and calls the empty dummy-procedure in the loop. Calls are taking longer when more rows are in the collection. When I just remove the call to dummy, performance is much better (the collection still contains the same number of records): Calling dummy: Not calling dummy: 11 0 81 0 158 0 Code to reproduce: Create Type t_tab Is Table Of VARCHAR2(10000); Create Type test_type As Object( tab t_tab, Member Procedure dummy ); Create Type Body test_type As Member Procedure dummy As Begin Null; --# Do nothing End dummy; End; Declare v_test_type test_type := New test_type( New t_tab() ); Procedure run_test As start_time NUMBER := dbms_utility.get_time; Begin For i In 1 .. 200 Loop v_test_Type.tab.Extend; v_test_Type.tab(v_test_Type.tab.Last) := Lpad(' ', 10000); v_test_Type.dummy(); --# Removed this line in second test End Loop; dbms_output.put_line( dbms_utility.get_time - start_time ); End run_test; Begin run_test; run_test; run_test; End; I tried with both 10g and 11g. Can anyone explain/reproduce this behavior?

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  • Determine caller within stored proc or trigger

    - by Mike Clark
    I am working with an insert trigger within a Sybase database. I know I can access the @@nestlevel to determine whether I am being called directly or as a result of another trigger or procedure. Is there any way to determine, when the nesting level is deeper than 1, who performed the action causing the trigger to fire? For example, was the table inserted to directly, was it inserted into by another trigger and if so, which one.

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