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• How to get max of composite data in SQL?

  - by Siddharth Sinha

  SELECT "Name""Month","Year","Value" from Table WHERE "Name" LIKE '%JERRY%' AND "Year" = (SELECT MAX("Year") FROM Table where "Name" LIKE '%JERRY%') AND "Month"= (SELECT MAX("Month") FROM Table where "Name" LIKE '%JERRY%' AND "Year"= (SELECT MAX("Year") FROM Table where "Name" LIKE '%JERRY%')) Table -- Name | Year | Month | Value ----------------------------- JERRY 2012 9 100 JERRY 2012 9 120 JERRY 2012 9 130 JERRY 2012 8 20 JERRY 2011 12 50 So i want the first three rows as output. As for the latest month for the latest year i need all the values. Can someone suggest a better cleaner query?

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• An attempt has been made to Attach or Add an entity that is not new Linq to Sql error

  - by Collin Oconnor

  I have a save function for my order entity that looks like this and it breaks on the sumbmitChanges line: public void SaveOrder ( Order order ) { if (order.OrderId == 0) orderTable.InsertOnSubmit(order); else if (orderTable.GetOriginalEntityState(order) == null) { orderTable.Attach(order); orderTable.Context.Refresh(RefreshMode.KeepCurrentValues , order); } orderTable.Context.SubmitChanges(); } The order entity contains two other entities; an Address entity and a credit card entity. Now i want these two entities to be null sometimes. Now my guess for why this is throwing an error is because that both of these entites that are inside order are null. If this is the case, How can I insert an new order into the database with both entities (Address and creditCard) being null.

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• Java - Collections.sort() performance

  - by msr

  Hello, Im using Collections.sort() to sort a LinkedList whose elements implements Comparable interface, so they are sorted in a natural order. In the javadoc documentation its said this method uses mergesort algorithm wich has n*log(n) performance. My question is if there is a more efficient algorithm to sort my LinkedList? The size of that list could be very high and sort will be also very frequent. Thanks!

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• How to optimize this SQL query for a rectangular region?

  - by Andrew B.

  I'm trying to optimize the following query, but it's not clear to me what index or indexes would be best. I'm storing tiles in a two-dimensional plane and querying for rectangular regions of that plane. The table has, for the purposes of this question, the following columns: id: a primary key integer world_id: an integer foreign key which acts as a namespace for a subset of tiles tileY: the Y-coordinate integer tileX: the X-coordinate integer value: the contents of this tile, a varchar if it matters. I have the following indexes: "ywot_tile_pkey" PRIMARY KEY, btree (id) "ywot_tile_world_id_key" UNIQUE, btree (world_id, "tileY", "tileX") "ywot_tile_world_id" btree (world_id) And this is the query I'm trying to optimize: ywot=> EXPLAIN ANALYZE SELECT * FROM "ywot_tile" WHERE ("world_id" = 27685 AND "tileY" <= 6 AND "tileX" <= 9 AND "tileX" >= -2 AND "tileY" >= -1 ); QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------- Bitmap Heap Scan on ywot_tile (cost=11384.13..149421.27 rows=65989 width=168) (actual time=79.646..80.075 rows=96 loops=1) Recheck Cond: ((world_id = 27685) AND ("tileY" <= 6) AND ("tileY" >= (-1)) AND ("tileX" <= 9) AND ("tileX" >= (-2))) -> Bitmap Index Scan on ywot_tile_world_id_key (cost=0.00..11367.63 rows=65989 width=0) (actual time=79.615..79.615 rows=125 loops=1) Index Cond: ((world_id = 27685) AND ("tileY" <= 6) AND ("tileY" >= (-1)) AND ("tileX" <= 9) AND ("tileX" >= (-2))) Total runtime: 80.194 ms So the world is fixed, and we are querying for a rectangular region of tiles. Some more information that might be relevant: All the tiles for a queried region may or may not be present The height and width of a queried rectangle are typically about 10x10-20x20 For any given (world, X) or (world, Y) pair, there may be an unbounded number of matching tiles, but the worst case is currently around 10,000, and typically there are far fewer. New tiles are created far less frequently than existing ones are updated (changing the 'value'), and that itself is far less frequent that just reading as in the query above. The only thing I can think of would be to index on (world, X) and (world, Y). My guess is that the database would be able to take those two sets and intersect them. The problem is that there is a potentially unbounded number of matches for either for either of those. Is there some other kind of index that would be more appropriate?

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• MySQL, SQL Select Statement, Where with OR... What's wrong with this?

  - by nobosh

  I'm looking for help with my query below. which is never returning anything for veggie... Is the way I have my WHERE statement written valid? SELECT * FROM newsfeed INNER JOIN newsfeedaction ON newsfeed.newsfeedactionid = newsfeedaction.newsFeedActionID INNER JOIN person ON newsfeed.personID = person.personID LEFT OUTER JOIN food ON newsfeed.foodID = food.foodID LEFT OUTER JOIN veggie ON newsfeed.veggieID = veggie.veggieID WHERE ( newsfeed.veggieID IS NOT NULL AND veggie.deleted = 'N' ) OR ( newsfeed.foodID IS NOT NULL AND food.deleted = 'N')

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• How do I get a linq to sql group by query into the asp.net mvc view?

  - by Brad Wetli

  Sorry for the newbie question, but I have the following query that groups parking spaces by their garage, but I can't figure out how to iterate the data in the view. I guess I should strongly type the view but am a newbie and having lots of problems figuring this out. Any help would be appreciated. Public Function FindAllSpaces() Implements ISpaceRepository.FindAllSpaces Dim query = _ From s In db.spaces _ Order By s.name Ascending _ Group By s.garageid Into spaces = Group _ Order By garageid Ascending Return query End Function The controller is taking the query object as is and putting it into the viewdata.model and as stated the view is not currently strongly typed as I haven't been able to figure out how to do this. I have run the query successfully in linqpad.

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• Caching Mysql database for better performance

  - by kobey

  Hi, I'm using Amazon cloud and I've performance issue since the HDD is not located on my machine. My database is small (~500MB) and I can afford to keep it all in my RAM. I do not want to keep queries in my RAM, i need all the tables there. How can i do it? Thanks, Koby P.S. I'm using ubuntu server...

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• How do I do a where clause in sql and return a count back?

  - by chobo2

  Hi I am using mssql and I want to make a query that returns a count back with a where clause. Like say I have a product Table ProductId ProductName Active So how would I make it I have like Select Count(*) From Product now I don't know how to filter it so it only could if Active = true; So if there are 3 active products then it would return a count of 3 even if there is a hundred rows in the db and the other 97 are only not active. so the where clause would be probably like where active = true I am not sure how to put them together though.

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• SQL Server: How to call a UDF, if available?

  - by Ian Boyd

  Most systems will have a user-defined function (UDF) available. Some will not. i want to use the UDF if it's there: SELECT Users.*, dbo.UserGroupMembershipNames(Users.UserID) AS MemberOfGroupNames FROM Users Otherwise fallback to the acceptable alternative SELECT Users.*, (SELECT TOP 1 thing FROM Something WHERE Something.ID = Users.UserID) AS MemberGroupNames FROM Users How do? My first attempt, using the obvious solution, of course failed: SELECT Users.*, CASE WHEN (OBJECT_ID('dbo.UserGroupMembershipNames') IS NOT NULL) THEN dbo.UserGroupMembershipNames(Users.UserID) ELSE (SELECT TOP 1 thing FROM Something WHERE Something.ID = Users.UserID) END AS MemberOfGroupNames FROM Users for reasons beyond me

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• Why does LINQ-to-SQL Paging fail inside a function?

  - by ssg

  Here I have an arbitrary IEnumerable<T>. And I'd like to page it using a generic helper function instead of writing Skip/Take pairs every time. Here is my function: IEnumerable<T> GetPagedResults<T>(IEnumerable<T> query, int pageIndex, int pageSize) { return query.Skip((pageIndex - 1) * pageSize).Take(pageSize); } And my code is: result = GetPagedResults(query, 1, 10).ToList(); This produces a SELECT statement without TOP 10 keyword. But this code below produces the SELECT with it: result = query.Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList(); What am I doing wrong in the function?

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• What's the best way to select max over multiple fields in SQL?

  - by allyourcode

  The I kind of want to do is select max(f1, f2, f3). I know this doesn't work, but I think what I want should be pretty clear (see update 1). I was thinking of doing select max(concat(f1, '--', f2 ...)), but this has various disadvantages. In particular, doing concat will probably slow things down. What's the best way to get what I want? update 1: The answers I've gotten so far aren't what I'm after. max works over a set of records, but it compares them using only one value; I want max to consider several values, just like the way order by can consider several values. update 2: Suppose I have the following table: id class_name order_by1 order_by_2 1 a 0 0 2 a 0 1 3 b 1 0 4 b 0 9 I want a query that will group the records by class_name. Then, within each "class", select the record that would come first if you ordered by order_by1 ascending then order_by2 ascending. The result set would consist of records 2 and 3. In my magical query language, it would look something like this: select max(* order by order_by1 ASC, order_by2 ASC) from table group by class_name

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• SQL Query Syntax : Using table alias in a count is invalid? Why?

  - by contactmatt

  Could someone please explain to me why the following query is invalid? I'm running this query against an Oracle 10g database. select count(test.*) from my_table test; I get the following error: ORA-01747: invalid user.table.column, table.column, or column specification however, the following two queries are valid. select count(test.column) from my_table test; select test.* from my_table test;

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• Are bit operations quick?

  - by flashnik

  I'm dealing with a problem which needs to work with a lot of data. Currently its' values are represented as unsigned int. I know that real values do not exceed some limit, say 1000. That means that I can use unsigned short to store it. One profit is that it'll use less space. Do I have to pay for it by loosing in performance? Another assumption. I decided to store data as short but all calling functions use int, so I need to convert between these datatypes when storing/extracting values. Wiil the performance lost be dramatic? Third assumption. Due to great wish to econom memory I decided to use not short but just 10 bits packed into array of unsigned int. What will happen in this case comparing with previous ones?

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• Lack of ImageList in MenuStrip and performance issues

  - by Ivan

  MenuStrip doesn't support using ImageList images. What are performance issues of this? Are there chances of using too much GDI resources and slow-downs? How many items should be considered acceptable, after which one should implement custom control that draws images from ImageList?

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• [SQL-SERVER 2008]how to convert a column value to uppercase before inserting?

  - by krishna

  For example if there is a column named 'code' in which the data should only be in uppercase, how to ensure that in before insert trigger ?

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• How can I load class's part using linq to sql without anonymous class or additional class?

  - by ais

  class Test { int Id{get;set;} string Name {get;set;} string Description {get;set;} } //1)ok context.Tests.Select(t => new {t.Id, t.Name}).ToList().Select(t => new Test{Id = t.Id, Name = t.Name}); //2)ok class TestPart{ int Id{get;set;} string Name {get;set;} } context.Tests.Select(t => new TestPart{Id = t.Id, Name = t.Name}).ToList().Select(t => new Test{Id = t.Id, Name = t.Name}); //3)error Explicit construction of entity type 'Test' in query is not allowed. context.Tests.Select(t => new Test{Id = t.Id, Name = t.Name}).ToList(); Is there any way to use third variant?

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• What does really happen when we do a BEGIN TRAN in SQL Server 2005?

  - by Misnomer

  Hi all, I came across this issue or maybe something I didn't realize but I did a Begin Tran and had some code inside it and never ran a commit or rollback as I forgot about it. That caused all many of the database queries or even just a simple select top 1000 command were just sitting on loading..? Now it probably has put some locks on the tables I guess since it did not let me query them..but I just wanted to know what exactly happened and what are the practices to be followed here ?

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• How generate the SQL queries that match the JPA Entity CRUD operations at build time with Hibernate

  - by aravisski

  Given JPA annotated Entities, is it possible to generate (i.e. before runtime) the list of queries that will be performed by Hibernate for CRUD operations (performed against EntityManager) ? For named queries it is possible using org.hibernate.hql.QueryTranslator Any pointer into the Hibernate API will be appreciated.

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• How can I SELECT rows with MAX(Column value), DISTINCT by another column in SQL?

  - by Kaptah

  My table is: id home datetime player resource ---|-----|------------|--------|--------- 1 | 10 | 04/03/2009 | john | 399 2 | 11 | 04/03/2009 | juliet | 244 5 | 12 | 04/03/2009 | borat | 555 3 | 10 | 03/03/2009 | john | 300 4 | 11 | 03/03/2009 | juliet | 200 6 | 12 | 03/03/2009 | borat | 500 7 | 13 | 24/12/2008 | borat | 600 8 | 13 | 01/01/2009 | borat | 700 I need to select each distinct "home" holding the maximum value of "datetime". Result would be: id home datetime player resource ---|-----|------------|--------|--------- 1 | 10 | 04/03/2009 | john | 399 2 | 11 | 04/03/2009 | juliet | 244 5 | 12 | 04/03/2009 | borat | 555 7 | 13 | 24/12/2008 | borat | 600 8 | 13 | 01/01/2009 | borat | 700 I have tried: // 1 ..by the MySQL manual: SELECT DISTINCT home, id, datetime as dt, player, resource FROM topten t1 WHERE datetime = (SELECT MAX(t2.datetime) FROM topten t2 GROUP BY home ) GROUP BY daytime ORDER BY daytime DESC Doesn't work. Result-set has 130 rows although database holds 187. Result includes some dublicates of 'home'. // 2 ..join SELECT s1.id, s1.home, s1.datetime, s1.player, s1.resource FROM topten s1 JOIN (SELECT id, MAX(datetime) AS dt FROM topten GROUP BY id) AS s2 ON s1.id = s2.id ORDER BY daytime Nope. Gives all the records. // 3 ..something exotic: With various results.

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• Is there some performance issue between leaving empty ListProperties or using dynamic (expando) prop

  - by indiehacker

  Is there a datastore performance difference between adding dynamic properties of the expando class when they are needed for an entity or the simpler (for me) framework of just setting up all possible properties I might need from the start even though most instances will just be left empty. In my specific case I would be having 5-8 empty ReferenceList properties as 'overhead' that will be empty when I skip using expando class.

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• linq-to-sql "an attempt has been made to attach or add an entity that is not new"?

  - by Curtis White

  I've been getting several errors: cannot add an entity with a key that is already in use An attempt has been made to attach or add an entity that is not new, perhaps having been loaded from another datacontext In case 1, this stems from trying to set the key for an entity versus the entity. In case 2, I'm not attaching an entity but I am doing this: MyParent.Child = EntityFromOtherDataContext; I've been using using the pattern of wrap everything with a using datacontext. In my case, I am using this in a web forms scenario, and obviously moving the datacontext object to a class wide member variables solves this. My questions are thus 2 fold: How can I get rid of these errors and not have to structure my program in an odd way or pass the datacontext around while keeping the local-wrap pattern? I assume I could make another hit to the database but that seems very inefficient. Would most people recommend that moving the datacontext to the class wide scope is desirable for web pages?

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• beneficial in terms of performance

  - by Usama Khalil

  Hi, is it better to declare Webservice class object instances as static as the .asmx webservice classes have only static methods. what i want is that i declare and instantiate webservice asmx class as static in aspx Page Behind Class. and on every event call on that page i could perform operation against webservice methods. is it beneficial in terms of performance? Thanks Usama

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• Want to build simple SQL admin interface to change a few values in a table.

  - by Adam McC

  i am currently building a system in MSSQL 2K5. i have a table that holds information about certain insurance schemes such as overheads and other things. these values will change occasionally and currently i administer the database straight through the management Studio. i would like to build a simple interface that will allow my colleagues to change these values by selecting the company in a dropdown and the current values will populate. they can then edit these values and submit them to the database. is this possible in the current Visual Studio supplied with MSSQL server 2K5 or do i need to get another product. i am confident that with the help of stack overflow and google i can build this myself, but i need pointed in the right direction as to which environment would be easiest and best to start building it. Many thanks, adam

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• Generating my own SQL Server SSL Certificate

  - by Haoest

  I hear it's possible to make myself a test certificate with MakeCert from Windows SDK, but the beast is 1.5 GB, which I feel reluctant to download for a half-megabyte program. I do, however, have IIS Resource kit with me, which has selfssl to generate certificate for IIS. Will that work for SQL Server? Is there a more convenient way of generating myself an SSL certificate for SQL Server use? I even tried using CREATE CERTIFICATE with TSQL within SQL Server and then have it BACKUP into a file, but with no success. I must have confused the concept of certificate fundamentally. Any advice?

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• Any good GUI tool to easily create stored procs SQL server 2008 ?

  - by Munish Goyal

  The templates for stored-procs in SSMS do not auto-populate all input columns, again there is manual work involved. I am looking for something like right-click on table and say CREATE stored-proc, and then it allows to pick a template, based on which it can populate the parameters etc. and give check-box in GUI (like table designer, you can easily add/remove a column). Some support for change management with table undergoing alter or otherwise would also be helpful. Currently we manually write all stored-procs, which i think we should be able to save time and labor with automation. Any suggestion on other free 3rd party tools ?

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