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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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  • How to create a better tables Structure.

    - by user160820
    For my website i have tables Category :: id | name Product :: id | name | categoryid Now each category may have different sizes, for that I have also created a table Size :: id | name | categoryid | price Now the problem is that each category has also different ingredients that customer can choose to add to his purchased product. And these ingredients have different prices for different sizes. For that I also have a table like Ingredient :: id | name | sizeid | categoryid | price I am not sure if this Structure really normalized is. Can someone please help me to optimize this structure and which indexed do i need for this Structure?

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  • Syntax error in INSERT INTO statement

    - by user454563
    I wrote a program that connects to MS Access. When I fill in the fields and add a new item to Access the program fails. The exception is "Syntax error in INSERT INTO statement" Here is the relevant code. **************************************************************** AdoHelper.cs **************************************************************** using System; using System.Collections.Generic; using System.Text; using System.Data; using System.Data.OleDb; namespace Yad2 { class AdoHelper { //get the connection string from the app.config file //Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\Yad2.accdb static string connectionString = Properties.Settings.Default.DBConnection.ToString(); //declare the db connection static OleDbConnection con = new OleDbConnection(connectionString); /// <summary> /// To Execute queries which returns result set (table / relation) /// </summary> /// <param name="query">the query string</param> /// <returns></returns> public static DataTable ExecuteDataTable(string query) { try { con.Open(); OleDbCommand command = new OleDbCommand(query, con); System.Data.OleDb.OleDbDataAdapter tableAdapter = new System.Data.OleDb.OleDbDataAdapter(command); DataTable dt = new DataTable(); tableAdapter.Fill(dt); return dt; } catch (Exception ex) { throw ex; } finally { con.Close(); } } /// <summary> /// To Execute update / insert / delete queries /// </summary> /// <param name="query">the query string</param> public static void ExecuteNonQuery(string query) { try { con.Open(); System.Data.OleDb.OleDbCommand command = new System.Data.OleDb.OleDbCommand(query, con); command.ExecuteNonQuery(); } catch (Exception ex) { throw ex; } finally { con.Close(); } } /// <summary> /// To Execute queries which return scalar value /// </summary> /// <param name="query">the query string</param> public static object ExecuteScalar(string query) { try { con.Open(); System.Data.OleDb.OleDbCommand command = new System.Data.OleDb.OleDbCommand(query, con); /// here is the Excaption !!!!!!!!! return command.ExecuteScalar(); } catch { throw; } finally { con.Close(); } } } } **************************************************************************** **************************************************************************** DataQueries.cs **************************************************************************** using System; using System.Collections.Generic; using System.Text; using System.Data; namespace Yad2 { class DataQueries { public static DataTable GetAllItems() { try { string query = "Select * from Messages"; DataTable dt = AdoHelper.ExecuteDataTable(query); return dt; } catch (Exception ex) { throw ex; } } public static void AddNewItem(string mesNumber, string title , string mesDate , string contactMail , string mesType , string Details ) { string query = "Insert into Messages values(" + mesNumber + " , '" + title + "' , '" + mesDate + "' , '" + contactMail + "' , , '" + mesType + "' , '" + Details + "')"; AdoHelper.ExecuteNonQuery(query); } public static void DeleteDept(int mesNumber) { string query = "Delete from Item where MessageNumber=" + mesNumber; AdoHelper.ExecuteNonQuery(query); } } } *********************************************************************************************** plase help me .... why the program falls ?

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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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  • 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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  • Migrating Data to MSSQL 2008

    - by Fred Clown
    I am trying to migrate data from an Informix database to MSSQL 2008. I've got quite a lot of data to move. I've been try multiple methods to get the data over, and so far SQLBulkCopy in multiple chunks seems to be the fastest that I can find. Does anyone know of a faster means of getting the data over? I'm trying to cut down on the transfer time so that on my cut-over date I don't run out of time to do the full cut-over. Thanks.

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  • How to handle Foreign key for optional field in .NET

    - by brz dot net
    What is the best way to handle following situation? A dropdown(for master table) is optional in a particular form. But, In database table the field is constrained with foreign key. If user don't select from dropdown then It creates problem because of foreign key. One solution is to create default option in master table and use it in case of blank selection. but in dropdown, we need to handle this to show on top. Is it perfect solution? Is there any other optimized solution for this? Thanks

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  • Foreign Keys and Primary Keys at the same time

    - by Bader
    hello , i am trying to create table (orderdetails) , the table has two FKs and PKs at the same keys here is my code create table OrderDetails2 ( PFOrder_ID Number(3) PFProduct_ID Number(3) CONSTRAINT PF PRIMARY KEY (PFOrder_ID,PFProduct_ID), CONSTRAINT FK_1 FOREIGN KEY (PFProudct_ID) REFERENCES Product(Product_ID), CONSTRAINT FK_2 FOREIGN KEY (PFOrder_ID) REFERENCES Orderr(Order_ID) ); i am using Oracle express , a problem pops when i run the code , here is it ORA-00907: missing right parenthesis what is the problem ?

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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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  • SQLException: incorrect syntax near '2'.

    - by Tobechukwu Ezenachukwu
    whenever I call the "ExecuteNonQuery" command on the following CommandText, I get the above SQLException myCommand.CommandText = "INSERT INTO fixtures (round_id, matchcode, date_utc, time_utc, date_london, time_london, team_A_id, team_A, team_A_country, team_B_id, team_B, team_B_country, status, gameweek, winner, fs_A, fs_B, hts_A, hts_B, ets_A, ets_B, ps_A, ps_B, last_updated) VALUES (" _ & round_id & "," & match_id & "," & date_utc & ",'" & time_utc & "'," & date_london & ",'" & time_london & "'," & team_A_id & ",'" & team_A_name & "','" & team_A_country & "'," & team_B_id & ",'" & team_B_name & "','" & _ team_B_country & "','" & status & "'," & gameweek & ",'" & winner & "'," & fs_A & "," & fs_B & "," & hts_A & "," & hts_B & "," & ets_A & "," & ets_B & "," & ps_A & "," & ps_B & "," & last_updated & ")" But whenever, i remove the last table item - "last_updated", the error disappears. Please help me resolve this issue. Is there any special treatment to be given to datetime fields??? Thanks for your help

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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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  • DB Interface Design Optimization: Is it better to optimise for Fewer requests of smaller data size?

    - by Overflow
    The prevailing wisdom in webservices/web requests in general is to design your api such that you use as few requests as possible, and that each request returns therefore as much data as is needed In database design, the accepted wisdom is to design your queries to minimise size over the network, as opposed to minimizing the number of queries. They are both remote calls, so what gives?

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  • Database Design Question: GUID + Natural Numbers

    - by Alan
    For a database I'm building, I've decided to use natural numbers as the primary key. I'm aware of the advantages that GUID's allow, but looking at the data, the bulk of row's data were GUID keys. I want to generate XML records from the database data, and one problem with natural numbers is that I don't want to expose my database key's to the outside world, and allow users to guess "keys." I believe GUID's solve this problem. So, I think the solution is to generate a sparse, unique iD derived from the natural ID (hopefully it would be 2-way), or just add an extra column in the database and store a guid (or some other multibyte id) The derived value is nicer because there is no storage penalty, but it would be easier to reverse and guess compared to a GUID. I'm (buy) curious as to what others on SO have done, and what insights they have.

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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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  • 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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  • 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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  • 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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  • Losing scope for DataContex using LINQToSQL intermediately

    - by greektreat
    I am having a weird Situation with my DataConext. All My code is in C# I have a DLL project for my data access layer and business Layer which and Winforms project for my UI layer. My Data access Layer's Namespace is xxx.Data this is where have my xxx.dbml I also have xxx.Data.BusinessObjects name space of course for my business object in that project In my UI Layer I have these namespaces xxxApp(for Forms), xxxApp.Controls (For Controls) I have lost scope of the DataContext, it was accessible now when I do a Rebuild Solution I sometimes get compile errors saying for example: Error 34 'xxx.Data.xxxDataContext' does not contain a definition for 'SubmitChanges' and no extension method 'SubmitChanges' accepting a first argument of type 'xxx.Data.xxxDataContext' could be found (are you missing a using directive or an assembly reference?) Also intelisense doesn't recognize the methods and table classes from my xxxDataContext anymore I can access all object fine when I am in the DLL project but now in the Winforms project this is very strange. If anyone can help me out I would be extremely grateful!

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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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  • How can i pull an image and data from a Database?

    - by user1851377
    I am trying to pull data from a Database using C#.net and use a Foreach loop to make it visible on a page. Every time i run the code i only get one item that shows up when i know that there is at least 7 items in the DB. i have placed the code below for the C#. SqlConnection oConnection = new SqlConnection(ConfigurationManager.ConnectionStrings["HomeGrownEnergyConnectionString"].ToString()); string sqlEnergy = "Select * from Product p where p.ProductTypeId=3"; SqlCommand oCmd = new SqlCommand(sqlEnergy, oConnection); DataTable dtenergy = new DataTable(); SqlDataAdapter oDa = new SqlDataAdapter(oCmd); try { oConnection.Open(); ; oDa.Fill(dtenergy); } catch (Exception ex) { lblnodata.Text = ex.Message; return; } finally { oConnection.Close(); } DataTableReader results = dtenergy.CreateDataReader(); if (results.HasRows) { results.Read(); foreach(DataRow result in dtenergy.Rows) { byte[] imgProd = result["ThumnailLocation"] as byte[]; ID.Text = result["ProductID"].ToString(); Name.Text = result["Name"].ToString(); price.Text = FormatPriceColumn(result["Price"].ToString()); } } Here is the code for the asp.net. <div> <asp:Image ID="imgProd" CssClass="ProdImg" runat="server" /> <asp:Label runat="server" ID="ID" /> <asp:Label runat="server" ID="Name" /> <asp:Label runat="server" ID="price" /> <asp:TextBox ID="txtQty" MaxLength="3" runat="server" Width="30px" /> <asp:Button runat="server" ID="Addtocart" Text="Add To Cart" CommandName="AddToCart" ItemStyle-CssClass="btnCol" /> If someone could please help me that would be great thanks.

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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 would using a Temp table be faster than a nested query?

    - by Mongus Pong
    We are trying to optimise some of our queries. One query is doing the following: SELECT t.TaskID, t.Name as Task, '' as Tracker, t.ClientID, (<complex subquery>) Date, INTO [#Gadget] FROM task t SELECT TOP 500 TaskID, Task, Tracker, ClientID, dbo.GetClientDisplayName(ClientID) as Client FROM [#Gadget] order by CASE WHEN Date IS NULL THEN 1 ELSE 0 END , Date ASC DROP TABLE [#Gadget] (I have removed the complex subquery, cos I dont think its relevant other than to explain why this query has been done as a two stage process.) Now I would have thought it would be far more efficient to merge this down into a single query using subqueries as : SELECT TOP 500 TaskID, Task, Tracker, ClientID, dbo.GetClientDisplayName(ClientID) FROM ( SELECT t.TaskID, t.Name as Task, '' as Tracker, t.ClientID, (<complex subquery>) Date, FROM task t ) as sub order by CASE WHEN Date IS NULL THEN 1 ELSE 0 END , Date ASC This would give the optimiser better information to work out what was going on and avoid any temporary tables. It should be faster. But it turns out it is a lot slower. 8 seconds vs under 5 seconds. I cant work out why this would be the case as all my knowledge of databases imply that subqueries would always be faster than using temporary tables. Can anyone explain what could be going on!?!?

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