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• oracle sql query to list all the dates of previous month

  - by Suresh S

  Guys i have a requirement to list all the dates of the previous month like below 20101201 20101202 20101203 20101204 20101205 .. .. .. .. .. .. .. .. 20101231 kindly let me know if any better way to do than this query. select TO_CHAR(TRUNC(SYSDATE,'MM')-1,'YYYYMMDD')-(level-1) as EACH_DATE from dual A connect by level < (TO_NUMBER(TO_CHAR(TRUNC(SYSDATE,'MM')-1,'DD'))+1) Also please let me know the problem with this query it says "missing right parenthesis" SELECT /*+ PARALLEL (A,8) */ /*+ DRIVING_STATE */ TO_CHAR(TRUNC(TRUNC(SYSDATE,'MM')-1,'MM'),'MONYYYY') "MONTH", TYPE AS "TRAFF", COLUMN, A_COUN AS "A_COUNT",COST FROM DATA_P B WHERE EXISTS ( select TO_NUMBER(TO_CHAR(TRUNC(SYSDATE,'MM')-1,'YYYYMMDD')-(level-1)) EACH_DATE from dual A connect by level < TO_NUMBER(TO_CHAR(TRUNC(SYSDATE,'MM')-1,'DD')+1) WHERE A.EACH_DATE = B.DATE order by EACH_DATE ASC )

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• Use of private constructor to prevent instantiation of class?

  - by cringe

  Hi guys! Right now I'm thinking about adding a private constructor to a class that only holds some String constants. public class MyStrings { // I want to add this: private MyString() {} public static final String ONE = "something"; public static final String TWO = "another"; ... } Is there any performance or memory overhead if I add a private constructor to this class to prevent someone to instantiate it? Do you think it's necessary at all or that private constructors for this purpose are a waste of time and code clutter?

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• sql query need a help.

  - by benjamin button

  If i have a table with two fields.customer id and order. let's say i have in total order ID 1,2,3,4 all the customer can have all the four orders.like below 1234 1 1234 2 1234 3 1234 4 3245 3 3245 4 5436 2 5436 4 you can see above that 3245 customer doesnt have order id 1 and 2. how could i print in the query output like 3245 1 3245 2 5436 1 5436 3 EDIT: i dont order table but i have list of order's like we can hard code it in the query(1,2,3,4) i dont have an orders table.

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• How to limit columns returned by Django query ?

  - by PhilGo20

  That seems simple enough, but all Django Queries seems to be 'SELECT *' How do I build a query returning only a subset of fields ?

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• CoreData and many NSArrayController

  - by unixo

  In my CoreData Application, I've an outline view on left of main window, acting as source list (like iTunes); on the right I display a proper view, based on outline selection. Each view has its components, such as table view, connected to array controller, owned by the specific view. Very often different views display same data, for example, a table view of the same entity. From a performance point of view, is better to have a single array controller per entity and share it between all views or does CoreData cache avoid memory waste?

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• DataTable linq query iteration

  - by Ravi

  Hi, I want to Enumerate Linq Query. Below i specified example. EX: DataTable _slidingDataTable = new DataTable("test"); for(int i=0; i<5;i++) { DataRow row = _slidingDataTable.NewRow(); startPosition = DateTime.Now; for(int i=0; i<5;i++) { _slidingDataTable.Columns.Add("TransferTime"); row[columnName] = startPosition ; _slidingDataTable.Columns.Add("TransferData"); row[columnName] = "Test"+i; } _slidingDataTable.Rows.Add(row); } var query1 = from myRow in _slidingDataTable.AsEnumerable() where myRow.Field<DateTime>("TransferTime") == startPosition select myRow; This query output should be collection of rows. How to get collection row & iterate.

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• MySQL - How do I insert an additional where clause into this full-text search query

  - by Steven

  I want to add a WHERE clause to a full text search query (to limit to past 24 hours), but wherever I insert it I get Low Level Error. Is it possible to add the clause and if so, how? $query = "SELECT * WHERE story_time > time()-86400 AND MATCH (story_title) AGAINST ('".validate_input($_GET['q'])."' IN BOOLEAN MODE) AS Relevance FROM ".$config['db']['pre']."stories WHERE MATCH (story_title) AGAINST ('+".validate_input($_GET['q'])."' IN BOOLEAN MODE) HAVING Relevance > 0.2 ORDER BY Relevance DESC, story_time DESC LIMIT ".validate_input(($_GET['page']-1)*10).",10";

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• Use SQL query to populate property in nHibernate mapping file

  - by brainimus

  I have an object which contains a property that is the result of an SQL statement. How do I add the SQL statement to my nHibernate mapping file? Example Object: public class Library{ public int BookCount { get; set; } } Example Mapping File: <hibernate-mapping> <class name="Library" table="Libraries"> <property name="BookCount" type="int"> <- This is where I want the SQL query to populate the value. -> </class> </hibernate-mapping> Example SQL Query: SELECT COUNT(*) FROM BOOKS WHERE BOOKS.LIBRARY_ID = LIBRARIES.ID

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• Multiple calculations on the same set of data: ruby or database?

  - by Pierre

  Hi, I have a model Transaction for which I need to display the results of many calculations on many fields for a subset of transactions. I've seen 2 ways to do it, but am not sure which is the best. I'm after the one that will have the least impact in terms of performance when data set grows and number of concurrent users increases. data[:total_before] = Transaction.where(xxx).sum(:amount_before) data[:total_after] = Transaction.where(xxx).sum(:amount_after) ... or transactions = Transaction.where(xxx) data[:total_before]= transactions.inject(0) {|s, e| s + e.amount_before } data[:total_after]= transactions.inject(0) {|s, e| s + e.amount_after } ... Which one should I choose? (or is there a 3rd, better way?) Thanks, P.

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• JQuery Optimization: Is there any way to speed up the rendering of the FlexSelect control?

  - by Sephrial

  Greetings, I am new to jQuery, and I have a performance problem with the FlexSelect control where it takes about 5 seconds to render the dropdown control (in the renderDropdown() function). The dropdown list contains about 5000 element. I believe all the runtime is attributed to the following block of code: var list = this.dropdownList.html(""); $.each(this.results, function() { list.append($("<li/>").html(this.name)); }); Question: Are there any alternatives that would build this list of elements in a more inefficient manner?

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• Need help optimizing MYSQL query with join

  - by makeee

  I'm doing a join between the "favorites" table (3 million rows) the "items" table (600k rows). The query is taking anywhere from .3 seconds to 2 seconds, and I'm hoping I can optimize it some. Favorites.faver_profile_id and Items.id are indexed. Instead of using the faver_profile_id index I created a new index on (faver_profile_id,id), which eliminated the filesort needed when sorting by id. Unfortunately this index doesn't help at all and I'll probably remove it (yay, 3 more hours of downtime to drop the index..) Any ideas on how I can optimize this query? In case it helps: Favorite.removed and Item.removed are "0" 98% of the time. Favorite.collection_id is NULL about 80% of the time. SELECT `Item`.`id`, `Item`.`source_image`, `Item`.`cached_image`, `Item`.`source_title`, `Item`.`source_url`, `Item`.`width`, `Item`.`height`, `Item`.`fave_count`, `Item`.`created` FROM `favorites` AS `Favorite` LEFT JOIN `items` AS `Item` ON (`Item`.`removed` = 0 AND `Favorite`.`notice_id` = `Item`.`id`) WHERE ((`faver_profile_id` = 1) AND (`collection_id` IS NULL) AND (`Favorite`.`removed` = 0) AND (`Item`.`removed` = '0')) ORDER BY `Favorite`.`id` desc LIMIT 50;

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• Referencing outer query's tables in a subquery

  - by soulmerge

  Is it possible to reference an outer query in a subquery with MySQL? I know there are some cases where this is possible: SELECT * FROM table t1 WHERE t1.date = ( SELECT MAX(date) FROM table t2 WHERE t2.id = t1.id)` ); But I'm wondering if something like this could work: SELECT u.username, c._postCount FROM User u INNER JOIN ( SELECT p.user, COUNT(*) AS _postCount FROM Posting p --# This is the reference I would need: WHERE p.user = u.id ) c ON c.user = u.id WHERE u.joinDate < '2009-10-10'; I know I could achieve the same using a GROUP BY or by pulling the outer WHERE clause into the sub-query, but I need this for automatic SQL generation and cannot use either alternative for various other reasons.

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• MySQL: Efficient Blobbing?

  - by feklee

  I'm dealing with blobs of up to - I estimate - about 100 kilo bytes in size. The data is compressed already. Storage engine: InnoDB on MySQL 5.1 Frontend: PHP (Symfony with Propel ORM) Some questions: I've read somewhere that it's not good to update blobs, because it leads to reallocation, fragmentation, and thus bad performance. Is that true? Any reference on this? Initially the blobs get constructed by appending data chunks. Each chunk is up to 16 kilo bytes in size. Is it more efficient to use a separate chunk table instead, for example with fields as below? parent_id, position, chunk Then, to get the entire blob, one would do something like: SELECT GROUP_CONCAT(chunk ORDER BY position) FROM chunks WHERE parent_id = 187 The result would be used in a PHP script. Is there any difference between the types of blobs, aside from the size needed for meta data, which should be negligible.

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• Minimizing Java Thread Context Switching Overhead

  - by binil

  I have a Java application running on Sun 1.6 32-bit VM/Solaris 10 (x86)/Nahelem 8-core(2 threads per core). A specific usecase in the application is to respond to some external message. In my performance test environment, when I prepare and send the response in the same thread that receives the external input, I get about 50 us advantage than when I hand off the message to a separate thread to send the response. I use a ThreadPoolExecutor with a SynchronousQueue to do the handoff. In your experience what is the acceptable delay between scheduling a task to a thread pool and it getting picked up for execution? What ideas had worked for you in the past to try improve this?

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• Adding more namespace in the code file affects performace ?

  - by Harikrishna

  If we imports more namespace in the code file(cs file) then it affects on perfomance ? Like we should add namespace in the cs file as needed. That is adding more namespace in the cs file affects performance ? Like using System; using System.Data.Sql; using System.Collections.Generic; using System.Data; using System.IO; using System.Linq; using System.Text.RegularExpressions; using System.Windows.Forms; using System.Xml; using System.Data.SqlClient; using System.ComponentModel;

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• Query To retrieve Desc. From Id In Linq

  - by Biswo

  I m new in Linq and i didnt understang this query Db.Enum_Countries .Where(p=p.id==id) .Single() .Title) Can you help me....

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• SQL query to select distinct record with 2 or more repetition in another field

  - by kyohiros

  So I have this table of book orders, it contains 2 columns, one is the order ID(primary key) and another is the ID of the book that the customer ordered. For example: | OrderID | BookID | | 0001 | B002 | | 0002 | B005 | | 0003 | B002 | | 0004 | B003 | | 0005 | B005 | | 0006 | B002 | | 0007 | B002 | What I want is to get the IDs of the books that got 2 or more purchases/orders, for example if I run the SQL query against the above data, I would get this as the result: | BookID | | B002 | | B005 | I don't know if this can be archived in SQL or I have to built a simpler statement and repetitive run the query against all the records in another language. I need some help and thanks for reading my question.

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• How can I intercept a Tomcat request at socket level?

  - by Miguel Pardal

  Hi, I'm doing a performance study for a web application framework running on Apache Tomcat 6. I'm trying to measure the time overhead of handling HTTP requests. What I would like to do is: / // just before first request byte is read long t1 = System.nanoTime(); // request is processed... // just after final byte is written to response long t2 = System.nanoTime(); / Then I would compute the total time (t2 - t1). Is there a way to do this? Thanks for your help!

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• Django: How/Where to store a value for a session without unnecessary DB hits

  - by GerardJP

  Hi all, I have an extended userprofile with AUTH_PROFILE_MODULE (ref: http://tinyurl.com/yhracqq) I would like to set a user.is_guru() method similar to user.is_active(). This would results for al views (or rather templates) to e.g. disable/enable certain user messages, displaying of widgets, etc. The boolean is stored in the extended user profile model, but I want to avoid hitting the DB for every view. So the questions is .. Do I use a context_processor, a template tag, session_dict or what have you to, possible cached, store this info for the duration of the users visit. Note: I dont have performance issues, so it's definitely filed under premature optimization. I just want to avoid generating extra work in the future :). Any pointers are very welcome. Thanx and greetz! Gerard.

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• What is the fastest way to compare 2 rows in SQL?

  - by Swoosh

  I have 2 different databases. Upon changing something in the big one (i don't have access to), i get some rows imported in my databases in a similar HUGE table. I have a job checking for records in this table, and if any, execute a stored procedure, process and delete from table. Performance. (Huge amount of data) I would like to know what is the fastest way to know if something has changed using let's say 2 imported rows with 100 columns each. Don't have FK-s, don't need. Chances are, that even though I have records in my table, nothing has actually changed. Also. Let's say there is actually changed something. Is it possible for example to check only for changes inside datetime columns? Thanks

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• Help me write a nicer SQL query in Rails

  - by Sainath Mallidi

  Hi, I am trying to write an SQL query to update some of the attributes that are regularly pulled from source. the output will be a text file with the following fields: author, title, date, popularity I have two tables to update one is the author information and the other is popularity table. And the Author Active Record object has one popularity. Currently I'm doing it like this.\ arr.each { |x| x = x.split(" ") results = Author.find_by_sql("SELECT authors.id FROM authors, priorities WHERE authors.id=popularity.authors_id AND authors.author = x[0]") results[0].popularity.update_attribute("popularity", x[3]) I need two tables because the popularity keeps changing, and I need only the top 1000 popular ones, but I still need to keep the previously popular ones also. Is there any nicer way to do this, instead of one query for every new object. Thanks.

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• sql query where parameters null not null

  - by Laziale

  I am trying to do a sql query and to build the where condition dynamically depending if the parameters are null or no. I have something like this: SELECT tblOrder.ProdOrder, tblOrder.Customer FROM tblOrder CASE WHEN @OrderId IS NOT NULL THEN WHERE tblOrder.OrderId = @OrderId ELSE END CASE WHEN @OrderCustomer IS NOT NULL THEN AND tblOrder.OrderCustomer = @OrderCustomer ELSE END END This doesn't work, but this is just a small prototype how to assemble the query, so if the orderid is not null include in the where clause, or if the ordercustomer is not null include in the where clause. But I see problem here, for example if the ordercustomer is not null but the orderid is null, there will be error because the where keyword is not included. Any advice how I can tackle this problem. Thanks in advance, Laziale

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• How can I improve the below query?

  - by Newbie

  I have the following input. INPUT: TableA ID Sentences --- ---------- 1 I am a student 2 Have a nice time guys! What I need to do is to extract the words from the sentence(s) and insert each individual word in another table OUTPUT: SentenceID WordOccurance Word ---------- ------------ ----- 1 1 I 1 2 am 1 3 a 1 4 student 2 1 Have 2 2 a 2 3 nice 2 4 time 2 5 guys! I was able to get the answer by using the below query ;With numCTE As ( Select rn = 1 Union all Select rn+1 from numCTE where rn<1000) select SentenceID=id, WordOccurance=row_number()over(partition by TableA.ID order by rn), Word = substring(' '+sentences+' ', rn+1, charindex(' ',' '+sentences+' ', rn+1)-rn-1) from TableA join numCTE on rn <= len(' '+sentences+' ') where substring(' '+sentences+' ', rn,1) = ' ' order by id, rn How can I improve this query of mine.? Basically I am looking for a better solution than the one presented Thanks

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• Oracle SQL: Query results from previous X isoweeks () (where X might be > 52)

  - by tommy-o-dell

  How could I adapt this query to show the previous 61 weeks? (still exlcluding the current week). My query currently shows me the total weekly sales for 2010 grouped by ISO Week and ISO Year (exlcuding the current week). select to_char(order_date,'IYYY') as iso_year, to_char(order_date,'IW') as iso_week, sum(sale_amount) from orders where to_char(order_date,'IW') <> to_char(SYSDATE) and to_char(order_date,'IYYY') = 2010 group by to_char(order_date,'IYYY') to_char(order_date,'IW') I realize I could probably just omit the "2010" requirement, order by desc and limit results to a certain bnumber of rows. But that just doesn't seem right! Much appreciate any help pointing me in the right direction!

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• MySQL Query involving column names containing math operators

  - by devil_fingers

  I'm a MySQL scrub, and I have asked around and checked around the internet for what I'm sure will turn out to be something obvious, but I'm very frustrated with what I thought would be a very, very simple query not working. So here goes. Please be gentle. Basically, in a large database, some of the column names contain mathematical operators like "/" and "+." (Don't ask, it's not my database, I can't do anything about it). Here is the "essence" of my query (I took out the irrelevant stuff for the sake of this question): SELECT PlayerId, Season, WPA/LI AS WPALI FROM tht.stats_batting_master WHERE Season = "2010" AND teamid > 0 AND PA >= 502 GROUP BY playerid ORDER BY WPALI DESC When I run this, it returns "Unknown column 'LI' in 'field list'," I assume because it sees the "/" in WPA/LI as a division sign. Like I said, I'm sure this is easy enough to work around (it must be given how much this database is used), but I haven't' been able to figure out how. Thanks in advance for any help.

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