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  • LINQ - Using where or join - Performance difference ?

    - by Patrick Säuerl
    Hi Based on this question: http://stackoverflow.com/questions/3013034/what-is-difference-between-where-and-join-in-linq My question is following: Is there a performance difference in the following two statements: from order in myDB.OrdersSet from person in myDB.PersonSet from product in myDB.ProductSet where order.Persons_Id==person.Id && order.Products_Id==product.Id select new { order.Id, person.Name, person.SurName, product.Model,UrunAdi=product.Name }; and from order in myDB.OrdersSet join person in myDB.PersonSet on order.Persons_Id equals person.Id join product in myDB.ProductSet on order.Products_Id equals product.Id select new { order.Id, person.Name, person.SurName, product.Model,UrunAdi=product.Name }; I would always use the second one just because it´s more clear. My question is now, is the first one slower than the second one? Does it build a cartesic product and filters it afterwards with the where clauses ? Thank you.

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  • Techniques for querying a set of object in-memory in a Java application

    - by Edd Grant
    Hi All, We have a system which performs a 'coarse search' by invoking an interface on another system which returns a set of Java objects. Once we have received the search results I need to be able to further filter the resulting Java objects based on certain criteria describing the state of the attributes (e.g. from the initial objects return all objects where x.y z && a.b == c). The criteria used to filter the set of objects each time is partially user configurable, by this I mean that users will be able to select the values and ranges to match on but the attributes they can pick from will be a fixed set. The data sets are likely to contain <= 10,000 objects for each search. The search will be executed manually by the application user base probably no more than 2000 times a day (approx). It's probably worth mentioning that all the objects in the result set are known domain object classes which have Hibernate and JPA annotations describing their structure and relationship. Off the top of my head I can think of 3 ways of doing this: For each search persist the initial result set objects in our database, then use Hibernate to re-query them using the finer grained criteria. Use an in-memory Database (such as hsqldb?) to query and refine the initial result set. Write some custom code which iterates the initial result set and pulls out the desired records. Option 1 seems to involve a lot of toing and froing across a network to a physical Database (Oracle 10g) which might result in a lot of network and disk activity. It would also require the results from each search to be isolated from other result sets to ensure that different searches don't interfere with each other. Option 2 seems like a good idea in principle as it would allow me to do the finer query in memory and would not require the persistence of result data which would only be discarded after the search was complete. Gut feeling is that this could be pretty performant too but might result in larger memory overheads (which is fine as we can be pretty flexible on the amount of memory our JVM gets). Option 3 could be very performant but is something I would like to avoid as any code we write would require such careful testing that the time taken to acheive something flexible and robust enough would probably be prohibitive. I don't have time to prototype all 3 ideas so I am looking for comments people may have on the 3 options above, plus any further ideas I have not considered, to help me decide which idea might be most suitable. I'm currently leaning toward option 2 (in memory database) so would be keen to hear from people with experience of querying POJOs in memory too. Hopefully I have described the situation in enough detail but don't hesitate to ask if any further information is required to better understand the scenario. Cheers, Edd

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  • Accessing global variables within functions in PHP

    - by st3
    There are multiple times in one page where I need to connect and subsequently query a MySQL database, yet my code won't let me. I think it might be something to do with how my files are nested but it makes no sense. I am opening the SQL connection in the header file. The top of the offending page looks like the following: <?php $page_title = 'Dashboard'; include('templates/header.inc'); // includes a 'require_once('mysqli_connect.php') and a small query to the database; require_once('includes/functions.php'); require_once('includes/dashboard_sql.php'); // Contains functions which connect to database (which are failing.) ?> I get the PHP error Notice: Undefined variable: dbc in /Library/WebServer/Documents/pediatory_site/includes/dashboard_sql.php Where $dbc is the database connection defined in mysqli_connect.php. If anyone could help me out that would be great.

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  • Getting unique items from NSMutableArray

    - by Gidogeek
    Hi Guys, I have a question about Objective-C today involving NSMutableArray. Coming from a .net/c# background I'm having some trouble working with these things. Let's say I have an object called "Song" My song has 3 properties: Title Artist Genre I have a NSMutableArray or NSArray wich holds all my Song objects. How would I go about trying to 'query' my array to get a new array with only (Unique) Artists or Genre's. Where as in .net you would write a simple LINQ query with a DISTINCT clause, how would one solve this in Objective-C ? I'm guessing with predicates but am struggling to find a solution. Thanks in advance.

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  • How to access java collection, just like the table in the database, having indexes and LINQ-like que

    - by Shaman
    This task occurs from time to time in my projects. I need to handle a collection of some complex elements, having different attributes, such as login, password_hash, role, etc. And, I need to be able to query that collection, just like I query a table in the database, having only partial data. For example: get all users, with role "user". Or check, if there's a user with login "root" and role "superuser". Removing items, based on same data is also needed. The first attempt I've tried is to use Google collections, Apache collections, and lambdaj. All of them have very similar preicate mechanism, but with a great disadvantage: it is based on iteration, one by one, over the collection of items, which is not good, for often used collections, containing big amounts of data. Could you please suggest me some solution? Thanks.

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  • Disk IO Performance Limitations based on numbers of folders/files

    - by Josh
    I have an application where users are allowed to upload images to the server. Our Web Server is a windows 2008 server and we have a site (images.mysite.com) that points to a shared drive on a unix box. The code used to do the uploading is C# 3.5. The system currently supports a workflow where after a threshold is met a new subfolder can be generated. The question we have is how many files and/or subfolders can you have in a single folder before there is a degredation in performance - in serving the images up through IIS 7 and reading/writing through code?

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  • Select all rows where there is not a specific value in a different table

    - by JMC Creative
    This is a wordpress installation, but I think the question is more of a general sql question. First off, my sql skills are not great (I don't even know if I'm following the correct format for illustrating the db). I've got two tables: wp_posts : ID (pk) | post_name | ... ---------------------------- 45 | "Hello" 91 | "Funny" 16 | "Wheat" wp_postmeta : post_id (fk) | meta_key | meta_value | ... ------------------------------------------------ 45 | "_edit_lock" | 5789789834 45 | "fizzbizz" | "foobar" 91 | "_something" | "teve" 16 | "_edit_lock" | 8798756 I would to select all rows in wp_posts where there is NO corresponding row in wp_postmeta where meta_key = "fizzbizz" I originally had this query, but someone pointed out that it would not retrive ID = '16' in the above case. How would I correctly write the query? $pageposts = $wpdb->get_results(" SELECT * FROM wp_posts p JOIN wp_postmeta m ON p.ID = m.post_id WHERE m.meta_key <> 'fizzbizz' ORDER BY p.post_date DESC; ");

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  • Lots of pointer casts in QGraphicsView framework and performance

    - by kleimola
    Since most of the convenience functions of QGraphicsScene and QGraphicsItem (such as items(), collidingItems(), childItems() etc.) return a QList you're forced to do lots of qgraphicsitem_cast or static_cast and QGraphicsItem::Type() checks to get hold of the actual items when you have lots of different type of items in the scene. I thought doing lots of subclass casts were not a desirable coding style, but I guess in this case there are no other viable way, or is there? QList<QGraphicsItem *> itemsHit = someItem->collidingItems(Qt::IntersectsItemShape); foreach (QGraphicsItem *item, itemsHit) { if (item->type() == QGraphicsEllipseItem::type()) { QGraphicsEllipseItem *ellipse = qgraphicsitem_cast<QGraphicsEllipseItem *>(item); // do something } else if (item->type() == MyItemSubclass::type()) { MyItemSubClass *myItem = qgraphicsitem_cast<MyItemSubClass *>(item); // do something } // etc } The above qgraphicsitem_cast could be replaced by static_cast since correct type is already verified. When doing lots of these all the time (very dynamic scene), will the numerous casting affect performance beyond the normal if-else evaluation?

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  • Microsoft Access - Enter Parameter Value why?

    - by Jane Doe
    I am encountering a problem for my database. Here is the relationships of the database And tried to do the query for how many transactions have movie "Harry_Potter"? so I used SQL query: SELECT COUNT(td.movie) AS number_of_occurrence, td.transaction_number FROM TransactionDetails td, MovieDetails md WHERE md.movie = Harry_Potter But it asks for Harry_Potter enter parameter value why? The relevant SQL statements are CREATE TABLE TransactionDetails ( transaction_number INTEGER PRIMARY KEY, movie VARCHAR(30) NOT NULL, date_of_transaction DATE NOT NULL, member_number INTEGER NOT NULL ) CREATE TABLE MovieDetails ( movie VARCHAR(30) PRIMARY KEY, movie_type VARCHAR(3) NOT NULL, movie_genre VARCHAR(10) NOT NULL ) ALTER TABLE TransactionDetails ADD CONSTRAINT member_number_fk FOREIGN KEY (member_number) REFERENCES LimelightMemberDetails(member_number); ALTER TABLE TransactionDetails ADD CONSTRAINT transaction_number_drink_fk FOREIGN KEY (transaction_number) REFERENCES DrinkTransactionDetails(transaction_number); ALTER TABLE TransactionDetails ADD CONSTRAINT transaction_number_food_fk FOREIGN KEY (transaction_number) REFERENCES FoodTransactionDetails(transaction_number); ALTER TABLE TransactionDetails ADD CONSTRAINT movie_fk FOREIGN KEY (movie) REFERENCES MovieDetails (movie); Thank you for your help! If there is anything wrong with my database design please let me know! thank you!

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  • get n records at a time from a temporary table

    - by Claudiu
    I have a temporary table with about 1 million entries. The temporary table stores the result of a larger query. I want to process these records 1000 at a time, for example. What's the best way to set up queries such that I get the first 1000 rows, then the next 1000, etc.? They are not inherently ordered, but the temporary table just has one column with an ID, so I can order it if necessary. I was thinking of creating an extra column with the temporary table to number all the rows, something like: CREATE TEMP TABLE tmptmp AS SELECT ##autonumber somehow##, id FROM .... --complicated query then I can do: SELECT * FROM tmptmp WHERE autonumber>=0 AND autonumber < 1000 etc... how would I actually accomplish this? Or is there a better way? I'm using Python and PostgreSQL.

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  • MySQL, delete and index hint

    - by Manuel Darveau
    I have to delete about 10K rows from a table that has more than 100 million rows based on some criteria. When I execute the query, it takes about 5 minutes. I ran an explain plan (the delete query converted to select * since MySQL does not support explain delete) and found that MySQL uses the wrong index. My question is: is there any way to tell MySQL which index to use during delete? If not, what ca I do? Select to temp table then delete from temp table? Thank you!

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  • Get latest record from second table left joined to first table

    - by codef0rmer
    I have a candidate table say candidates having only id field and i left joined profiles table to it. Table profiles has 2 fields namely, candidate_id & name. e.g. Table candidates: id 1 2 and Table `profiles`: candidate_id name 1 Foobar 1 Foobar2 2 Foobar3 i want the latest name of a candidate in a single query which is given below: SELECT C.id, P.name FROM candidates C LEFT JOIN profiles P ON P.candidate_id = C.id GROUP BY C.id ORDER BY P.name; But this query returns: 1 Foobar 2 Foobar3 Instead of: 1 Foobar2 2 Foobar3

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  • effective counter for unique number of visits in PHP & MySQL

    - by Adnan
    Hello, I am creating a counter for unique number of visits on a post, so what I have until now is a table for storing data like this; cvp_post_id | cvp_ip | cvp_user_id In cases a registered user visits a post, for the first time a record is inserted with cpv_post_id and cvp_user_id, so for his next visit I query the table and if the record is available I do not count him as a new visitor. In cases of an anonymous user the same happens but now the cvp_ip and cpv_post_id are used. My concerns is that I do a query every time anyone visits a post for checking if there has been a visit, what would be a more effective way for doing this?

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  • Performance improvement to a big if clause in SQL Server function

    - by Miles D
    I am maintaining a function in SQL Server 2005, that based on an integer input parameter needs to call different functions e.g. IF @rule_id = 1 -- execute function 1 ELSE IF @rule_id = 2 -- execute function 2 ELSE IF @rule_id = 3 ... etc The problem is that there are a fair few rules (about 100), and although the above is fairly readable, its performance isn't great. At the moment it's implemented as a series of IF's that do a binary-chop, which is much faster, but becomes fairly unpleasant to read and maintain. Any alternative ideas for something that performs well and is fairly maintainable?

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  • Multiple connections to a MySQL database in a single PHP script.

    - by st3
    There are multiple times in one page where I need to connect and subsequently query a MySQL database, yet my code won't let me. I think it might be something to do with how my files are nested but it makes no sense. I am opening the SQL connection in the header file. The top of the offending page looks like the following: <?php $page_title = 'Dashboard'; include('templates/header.inc'); // includes a 'require_once('mysqli_connect.php') and a small query to the database; require_once('includes/functions.php'); require_once('includes/dashboard_sql.php'); // Contains functions which connect to database (which are failing.) ?> I get the PHP error Notice: Undefined variable: dbc in /Library/WebServer/Documents/pediatory_site/includes/dashboard_sql.php Where $dbc is the database connection defined in mysqli_connect.php. If anyone could help me out that would be great.

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  • Performance side effect with static internal Util classes?

    - by Fostah
    For a util class that contains a bunch of static functionality that's related to the same component, but has different purposes, I like to use static internal classes to organize the functionality, like so: class ComponentUtil { static class Layout { static int calculateX(/* ... */) { // ... } static int calculateY(/* ... */) { // ... } } static class Process { static int doThis(/* ... */) { // ... } static int doThat(/* ... */) { // ... } } } Is there any performance degradation using these internal classes vs. just having all the functionality in the Util class?

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  • Fetching a result twice with deferend name

    - by user1799842
    I have 1 table with tasks named opentask:columns: id,title,description,expires,creator_id,creator_name, executer_id, executer_name, priority_id, status_id1 table with users named user: with columns: user_id, username What I want is to create a query where there will be all columns from opentask table where the executer_id will be equal to the user_id of user table AND the creator_id will be equal to the user_id again. This creates a confusion because the first equality excludes the second.So I need somehow to create a query where I will include the usernames for the executer with something like where "opentask.executer_id=user_user_id" and at the same time I will include the username again (as a differend name?) for the creator with something like "where opentask.executer_id=user_user_id"So I try this, which of course I know that is missing something, can you help? SELECT DISTINCT id, title, description, expires, creator_id, executer_id, oc_opentask.priority_id, oc_opentask.status_id, priority_name, status_name, user_id, username, (SELECT username FROM oc_opentask, oc_user WHERE oc_opentask.creator_id=oc_user.user_id) AS username2 FROM oc_opentask, oc_opentask_priority, oc_user, oc_opentask_status WHERE oc_opentask.priority_id=oc_opentask_priority.priority_id AND oc_opentask.executer_id=oc_user.user_id AND oc_opentask.status_id=oc_opentask_status.status_id ORDER BY oc_opentask.expires DESC

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  • I can't understand GroupJoin where i will need it in database relationships.

    - by Freshblood
    Hello Everybody I am thinking 5-6 hours to understand something about GroupJoin. I am talking about query with linq for Database tables.I understand what Join and GroupJoin does but I really couldn't understand where i will need it.I feel that Join does all what i will need but if there is something which Join can't without GroupJoin so i feel that situation is meaningless or useless. For example: Persons table in relation with Phones and Phones table hold foreign keys of Persons and one person can have one more phone number.If we want to brings all persons who has phone numbers and who hasn't too so we will need GroupJOin but what for we will need this query ? Can u give me good reason , example or explenation for using GroupJoin ?

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  • Caching result of SELECT statement for reuse in multiple queries

    - by Andrew
    I have a reasonably complex query to extract the Id field of the results I am interested in based on parameters entered by the user. After extracting the relevant Ids I am using the resulting set of Ids several times, in separate queries, to extract the actual output record sets I want (by joining to other tables, using aggregate functions, etc). I would like to avoid running the initial query separately for every set of results I want to return. I imagine my situation is a common pattern so I am interested in what the best approach is. The database is in MS SQL Server and I am using .NET 3.5.

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  • Performance: Subquerry or Joining

    - by Auro
    HelloHello I got a little Question about Performance of a Subquerry /Joining another table INSERT INTO Original.Person ( PID, Name, Surname, SID ) ( SELECT ma.PID_new , TBL.Name , ma.Surname, TBL.SID FROM Copy.Person TBL , original.MATabelle MA WHERE TBL.PID = p_PID_old AND TBL.PID = MA.PID_old ); This is my SQL, now this thing runs around 1 million times or more. Now my question is what would be faster? if I change TBL.SID to (Select new from helptable where old = tbl.sid) or if I add helptable to the from and do the joining in the where? greets Auro

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  • Simple performance testing tool in C#?

    - by Tomas
    Hi, At first -I need to do it as my university project so I am not interested in using existing tools. I would like to know whether it is even possible to write a very simple tool that I could use for performance testing of web applications. It would only record actions (I do not know, maybe just packet sniffering?) and then replay. However I have basic idea (record packets on port 80 and sending them again), I do not know how to measure time for each transaction as they are not differentiated. Any help is greatly appreciated, thank you!

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