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• DB optimization to use it as a queue

  - by anony

  We have a table called worktable which has some columns(key(primary key), ptime, aname, status, content) we have something called producer which puts in rows in this table and we have consumer which does an order-by on the key column and fetches the first row which has status as 'pending'. The consumer does some processing on this row: 1. updates status to "processing" 2. does some processing using content 3. deletes the row we are facing contention issues when we try to run multiple consumers(probably due to the order-by which does a full table scan)... using Advanced queues would be our next step but before we go there we want to check what is the max throughput we can achieve with multiple consumers and producer on the table. What are the optimizations we can do to get the best numbers possible? Can we do an in-memory processing where a consumer fetches 1000 rows at a time processes and deletes? will that improve? What are other possibilities? partitioning of table? parallelization? Index organized tables?...

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• Are programming languages and methods ineffective? (assembler and C knowledge needed)

  - by b-gen-jack-o-neill

  Hi, for a long time, I am thinking and studying output of C language compiler in asemlber form, as well as CPU architecture. I know this may be silly to you, but it seems to me that something is very ineffective. Please, don´t be angry if I am wrong, and there is some reason I do not see for all these principles. I will be very glad if you tell me why is it designed this way. I actually trully believe I am wrong, I know the genius minds of people which get PCs together knew a reason to do so. What exactly, do you ask? I´ll tell you right away, I use C as a example: 1, Stack local scope memory allocation: So, typical local memory allocation uses stack. Just copy esp to ebp and than allocate all the memory via ebp. OK, I would understand this if you explicitly need allocate RAM by default stack values, but if I do understand it correctly, modern OS use paging as a translation layer between application and physical RAM, when adress you desire is further translated before reaching actuall RAM byte. So why don´t just say 0x00000000 is int a,0x00000004 is int b and so? And access them just by mov 0x00000000,#10? Becouse you wont actually access memory blocks 0x00000000 and 0x00000004 but those your OS set the paging tables to. Actually, since memory allocation by ebp and esp use indirect adressing, "my" way would be even faster. 2, Variable allocation duplicitly: When you run aaplication, Loader load its code into RAM. When you create variable, or string, compiler generates code that pushes these values on the top o stack when created in main. So there is actuall instruction for do so, and that actuall number in memory. So, there are 2 entries of the same value in RAM. One in fomr of instruction, second in form of actuall bytes in the RAM. But why? Why not to just when declaring variable count at which memory block it would be, than when used, just insert this memory location?

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• how to insert excel-2003 values into SQL2005 database?

  - by vas

  Are there any rules / guidelines for DATA form XLS sheets to be inserted into SQL- DB? I have a group of Excel templates in 2005.Each concerned cell in Excel template is named. When Excel sheets are filled, saved and submitted , the values are transferred to the database. Excel sheets have names for various cells that are to b e filled by the user EX:- for the total number of Milk in the Beginning a given month , there is an Excel Cell Named "mtsBpiPTR180" Total number of Milk in the Ending a given month , there is an Excel Cell Named **"mtsEpiPTR180"** I have added 2 new cells , named "mtsBpiPTR180PA" and "mtsEpiPTR180PA". Now I try to upload the Excel File. But I AM UNABLE TO SEE MY FILLED DATA FROM "mtsBpiPTR180PA" and "mtsEpiPTR180PA" INTO THE RELATED DB/table. The above 2 are empty in the DB/table, even though I have filled them and successfully filed the Excel sheets Now no matter how much I search in the DB/stored procs i am unable to the ACTUAL STORED PROC or how the Data form Excel sheet is inserted into Tables WHERE DATA FROM XLS is inserted into DB. So was wondering:- Are there any rules / guidelines for DATA form XLS sheets to be inserted into SQL- DB?

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• MySQL COUNT() total posts within a specific criteria?

  - by newbtophp

  Hey, I've been losing my hair trying to figure out what I'm doing wrong, let me explain abit about my MySQL structure (so you get a better understanding) before I go straight to the question. I have a simple PHP forum and I have a column in both tables (for posts and topics) named 'deleted' if it equals 0 that means its displayed (considered not deleted/exists) or if it equals 1 it hidden (considered deleted/doesn't exist) - bool/lean. Now, the 'specific criteria' I'm on about...I'm wanting to get a total post count within a specific forum using its id (forum_id), ensuring it only counts posts which are not deleted (deleted = 0) and their parent topics are not deleted either (deleted = 0). The column/table names are self explanatory (see my efforts below for them - if needed). I've tried the following (using a 'simple' JOIN): SELECT COUNT(t1.post_id) FROM forum_posts AS t1, forum_topics AS t2 WHERE t1.forum_id = '{$forum_id}' AND t1.deleted = 0 AND t1.topic_id = t2.topic_id AND t2.deleted = 0 LIMIT 1 I've also tried this (using a Subquery): SELECT COUNT(t1.post_id) FROM forum_posts AS t1 WHERE t1.forum_id = '{$forum_id}' AND t1.deleted = 0 AND (SELECT deleted FROM forum_topics WHERE topic_id = t1.topic_id) = 0 LIMIT 1 But both don't comply with the specific criteria. Appreciate all help! :)

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• Database (and ORM) choice for an small-medium size .NET Application

  - by jim

  I have a requirement to develop a .NET-based application whose data requirements are likely to exceed the 4 gig limit of SQL 2005 Express Edition. There may be other customers of the same application (in the future) with a requirement to use a specific DB platform (such as Oracle or SQL Server) due to in-house DBA expertise. Questions What RDBMS would you guys recommend? From the looks of it the major choices are PostGreSQL, MySQL or FireBird. I've only got experience of MYSQL from these. Which ORM tool (if any) would you recommend using - ideally one that can be swapped out between DB platforms with minimal effort? I like the look of the entity framework but unsure as to the degree to which platforms other than SQL Server are supported. If it helps, we'll be using the 3.5 version of the Framework. I'm open to the idea of using a tool such as NHibernate. On the other hand, if it's going to be easier, I'm happy to write my own stored procedures / DAL code - there won't be that many tables (perhaps 30-35).

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• MySQL: optimization of table (indexing, foreign key) with no primary keys

  - by Haradzieniec

  Each member has 0 or more orders. Each order contains at least 1 item. memberid - varchar, not integer - that's OK (please do not mention that's not very good, I can't change it). So, thera 3 tables: members, orders and order_items. Orders and order_items are below: CREATE TABLE `orders` ( `orderid` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT, `memberid` VARCHAR( 20 ), `Time` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP , `info` VARCHAR( 3200 ) NULL , PRIMARY KEY (orderid) , FOREIGN KEY (memberid) REFERENCES members(memberid) ) ENGINE = InnoDB; CREATE TABLE `order_items` ( `orderid` INT(11) UNSIGNED NOT NULL, `item_number_in_cart` tinyint(1) NOT NULL , --- 5 items in cart= 5 rows `price` DECIMAL (6,2) NOT NULL, FOREIGN KEY (orderid) REFERENCES orders(orderid) ) ENGINE = InnoDB; So, order_items table looks like: orderid - item_number_in_cart - price: ... 1000456 - 1 - 24.99 1000456 - 2 - 39.99 1000456 - 3 - 4.99 1000456 - 4 - 17.97 1000457 - 1 - 20.00 1000458 - 1 - 99.99 1000459 - 1 - 2.99 1000459 - 2 - 69.99 1000460 - 1 - 4.99 ... As you see, order_items table has no primary keys (and I think there is no sense to create an auto_increment id for this table, because once we want to extract data, we always extract it as WHERE orderid='1000456' order by item_number_in_card asc - the whole block, id woudn't be helpful in queries). Once data is inserted into order_items, it's not UPDATEd, just SELECTed. The questions are: I think it's a good idea to put index on item_number_in_cart. Could anybody please confirm that? Is there anything else I have to do with order_items to increase the performance, or that looks pretty good? I could miss something because I'm a newbie. Thank you in advance.

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• How can I improve this SQL to avoid several problems with its results?

  - by Josh Curren

  I am having some problems with trying to search. Currently this will only return results that have at least 1 row in the maintenance_parts table. I would like it to return results even if there are 0 parts rows. My second problem is that when you search for a vehicle and it should return multiple results (multiple maintenance rows) it will only return 1 result for that vehicle. Some Background Info: The user has 2 fields to fill out. The fields are vehicle and keywords. The vehicle field is meant to allow searching based on the make, model, VIN, truck number (often is 2 - 3 digits or a letter prefix followed by 2 digits), and a few other fields that belong to the truck table. The keywords are meant to search most fields in the maintenance and maintenance_parts tables (things like the description of the work, parts name, parts number). The maintenance_parts table can contain 0, 1, or more rows for each maintenance row. The truck table contains exactly 1 row for every maintenance row. A truck can have multiple maintenance records. "SELECT M.maintenance_id, M.some_id, M.type_code, M.service_date, M.mileage, M.mg_id, M.mg_type, M.comments, M.work_done, MATCH( M.comments, M.work_done) AGAINST( '$keywords' ) + MATCH( P.part_num, P.part_desc, P.part_ref) AGAINST( '$keywords' ) + MATCH( T.truck_number, T.make, T.model, T.engine, T.vin_number, T.transmission_number, T.comments) AGAINST( '$vehicle' ) AS score FROM maintenance M, maintenance_parts P, truck T WHERE M.maintenance_id = P.maintenance_id AND M.some_id = T.truck_id AND M.type_code = 'truck' AND ( (MATCH( T.truck_number, T.make, T.model, T.engine, T.vin_number, T.transmission_number, T.comments) AGAINST( '$vehicle' ) OR T.truck_number LIKE '%$vehicle%') OR MATCH( P.part_num, P.part_desc, P.part_ref) AGAINST( '$keywords' ) OR MATCH( M.comments, M.work_done) AGAINST( '$keywords' ) ) AND M.status = 'A' GROUP BY maintenance_id ORDER BY score DESC, maintenance_id DESC LIMIT 0, $limit"

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• Create an Oracle function that returns a table

  - by Craig

  I'm trying to create a function in package that returns a table. I hope to call the function once in the package, but be able to re-use its data mulitple times. While I know I create temp tables in Oracle, I was hoping to keep things DRY. So far, this is what I have: Header: CREATE OR REPLACE PACKAGE TEST AS TYPE MEASURE_RECORD IS RECORD ( L4_ID VARCHAR2(50), L6_ID VARCHAR2(50), L8_ID VARCHAR2(50), YEAR NUMBER, PERIOD NUMBER, VALUE NUMBER ); TYPE MEASURE_TABLE IS TABLE OF MEASURE_RECORD; FUNCTION GET_UPS( TIMESPAN_IN IN VARCHAR2 DEFAULT 'MONTLHY', STARTING_DATE_IN DATE, ENDING_DATE_IN DATE ) RETURN MEASURE_TABLE; END TEST; Body: CREATE OR REPLACE PACKAGE BODY TEST AS FUNCTION GET_UPS ( TIMESPAN_IN IN VARCHAR2 DEFAULT 'MONTLHY', STARTING_DATE_IN DATE, ENDING_DATE_IN DATE ) RETURN MEASURE_TABLE IS T MEASURE_TABLE; BEGIN SELECT ... INTO T FROM ... ; RETURN T; END GET_UPS; END TEST; The header compiles, the body does not. One error message is 'not enough values', which probably means that I should be selecting into the MEASURE_RECORD, rather than the MEASURE_TABLE. What am I missing?

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• How to store and collect data for mining such information as most viewed for last 24 hours, last 7 d

  - by Kirzilla

  Hello, Let's imagine that we have high traffic project (a tube site) which should provide sorting using this options (NOT IN REAL TIME). Number of videos is about 200K and all information about videos is stored in MySQL. Number of daily video views is about 1.5KK. As instruments we have Hard Disk Drive (text files), MySQL, Redis. Views top viewed top viewed last 24 hours top viewed last 7 days top viewed last 30 days top rated last 365 days How should I store such information? The first idea is to log all visits to text files (single file per hour, for example visits_20080101_00.log). At the beginning of each hour calculate views per video for previous hour and insert this information into MySQL. Then recalculate totals (for last 24 hours) and update statistics in tables. At the beginning of every day we have to do the same but recalculate for last 7 days, last 30 days, last 365 days. This method seems to be very poor for me because we have to store information about last 365 days for each video to make correct calculations. Is there any other good methods? Probably, we have to choose another instruments for this? Thank you.

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• Laravel check if id exists?

  - by devt204

  I've two columns in contents tables 1. id 2. content now this is what i'm trying to do Route::post('save', function() { $editor_content=Input::get('editor_content'); $rules = array('editor_content' => 'required'); $validator= Validator::make(Input::all(), $rules); if($validator->passes()) { //1. check if id is submitted? //2. if id exists update content table //3. else insert new content //create new instance $content= new Content; // insert the content to content column $content->content = $editor_content; //save the content $content->save(); // check if content has id $id=$content->id; return Response::json(array('success' => 'sucessfully saved', 'id' => $id)); } if($validator->fails()) { return $validator->messages() ; } }); i wanted to check if id has been already submit or checked i'm processing the request via ajax, and if id exists i wanted update the content column and if it doesn't i wanted to create new instance how do i do it ?

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• MSSQL Server using multiple ID Numbers

  - by vincer

  I have an web application that creates printable forms, these forms have a unique number on them, the problem is I have 2 forms that separate numbers need to be created for them. ie) Form1- Numbered 2000000-2999999 Form2- Numbered 3000000-3999999 dbo.test2 - is my form information table Tsel - is my autoinc table for the 3000000 series numbers Tadv - is my autoinc table for the 2000000 series numbers What I have done is create 2 tables with just autoinc row (one for 2000000 series numbers and one for 3000000 series numbers), I then created a trigger to add a record to the coresponding table, read back the autoinc number and add it to my table that stores the form information including the just created autoinc number for the right series of forms. Although it does work, I'm concerned that the numbers will get messed up under load. I'm not sure the @@IDENTITY will always return the right value when many people are using the system. (I cannot have duplicates and I need to use the numbering form show above. Thanks for any help See code below. ** TRIGGER ** CREATE TRIGGER MAKEANID2 ON dbo.test2 AFTER INSERT AS SET NOCOUNT ON declare @someid int declare @someid2 int declare @startfrom int declare @test1 varchar(10) select @someid=@@IDENTITY select @test1 = (Select name1 from test2 where sysid = @someid ) if @test1 = 'select' begin insert into Tsel Default values select @someid2 = @@IDENTITY end if @test1 = 'adv' begin insert into Tadv Default values select @someid2 = @@IDENTITY end update test2 set name2=(@someid2) where sysid = @someid SET NOCOUNT OFF

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• Css absolute position don't work in MS WORD

  - by Tim

  Hello! This is a sample: <html> <head> <title>word test</title> </head> <body> <div style='position: absolute; width: 30px; height: 50px; top: 100px; left: 20px; border-color: black; border-width: 1px; border-style: solid;'> <p>Hello!</p> </div> </body> </html> Save it as "word.doc" and open in MS WORD. Absolute position don't work! Div is rendered on the top of document and with 100% width. Why? I can't use a html tables. Version on ms word: 2003

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• How to synchronize two (or n) replication processes for SQL Server databases?

  - by Yauheni Sivukha

  There are two master databases and two read-only copies updated by standard transactional replication. It is needed to map some entity from both read-only databases, lets say that A databases contains orders and B databases contains lines. The problem is that replication to one database can lag behind replication of second database, and at the moment of mapping R-databases will have inconsistent data. For example. We stored 2 orders with lines at 19:00 and 19:03. Mapping process started at 19:05, but to the moment of mapping A database replication processed all changes up to 19:03, but B database replication processed only changes up to 19:00. After mapping we will have order entity with order as of 19:03 and lines as of 19:00. The troubles are guaranteed:) In my particular case both databases have temporal model, so it is possible to fetch data for every time slice, but the problem is to identify time of latest replication. Question: How to synchronize replication processes for several databases to avoid situation described above? Or, in other words, how to compare last time of replication in each database? UPD: The only way I see to synchronize is to continuously write timestamps into service tables in each database and to check these timestamps on replicated servers. Is that acceptable solution?

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• What is a better, cleaner way of using List<T>

  - by Tim Meers

  I'm looking to implement a few nicer ways to use List in a couple of apps I'm working on. My current implementation looks like this. MyPage.aspx.cs protected void Page_Load(object sender, EventArgs e) { BLL.PostCollection oPost = new BLL.PostCollection(); oPost.OpenRecent(); rptPosts.DataSource = oArt; rptPosts.DataBind(); } BLL Class(s) public class Post { public int PostId { get; set; } public string PostTitle { get; set; } public string PostContent { get; set; } public string PostCreatedDate { get; set; } public void OpenRecentInitFromRow(DataRow row) { this.PostId = (int) row["id"]; this.PostTitle = (string) row["title"]; this.PostContent = (string) row["content"]; this.PostCreatedDate = (DateTime) row["createddate"]; } } public class PostCollection : List<Post> { public void OpenRecent() { DataSet ds = DbProvider.Instance().Post_ListRecent(); foreach (DataRow row in ds.Tables[0].Rows) { Post oPost = new Post(); oPost.OpenRecentInitFromRow(row); Add(oPost); } } } Now while this is working all well and good, I'm just wondering if there is any way to improve it, and just make it cleaner that having to use the two different classes do to something I think can happen in just one class or using an interface.

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• jQueryUI dialog width

  - by user35295

  Fiddle Full Screen Example I use jQuery dialog to open tables. Some of them have a large amount of text and they tend to be too long and go way off the screen. How can I make the dialog wider if the table is too long like the first one in the fiddle? I've tried width:'auto' but it seems to just occupy the entire screen. HTML: <button class='label'>Click</button><div class='dialog'><p><table>.....</table></div> <button class='label'>Click</button><div class='dialog'><p><table>.....</table></div> Javascript: $(document).ready(function(){ $('.label').each(function() { var dialogopen = $(this).next(".dialog"); dialogopen.dialog({width:'auto',autoOpen: false,modal: true, open: function(){ jQuery('.ui-widget-overlay').bind('click',function(){ dialogopen.dialog('close'); }) } }); $(this).click(function(){ dialogopen.dialog('open'); return false; } ); }); });

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• performance issue: difference between select s.* vs select *

  - by kamil

  Recently I had some problem in performance of my query. The thing is described here: poor Hibernate select performance comparing to running directly - how debug? After long time of struggling, I've finally discovered that the query with select prefix like: select sth.* from Something as sth... Is 300x times slower then query started this way: select * from Something as sth.. Could somebody help me, and asnwer why is that so? Some external documents on this would be really useful. The table used for testing was: SALES_UNIT table contains some basic info abot sales unit node such as name and etc. The only association is to table SALES_UNIT_TYPE, as ManyToOne. The primary key is ID and field VALID_FROM_DTTM which is date. SALES_UNIT_RELATION contains relation PARENT-CHILD between sales unit nodes. Consists of SALES_UNIT_PARENT_ID, SALES_UNIT_CHILD_ID and VALID_TO_DTTM/VALID_FROM_DTTM. No association with any tables. The PK here is ..PARENT_ID, ..CHILD_ID and VALID_FROM_DTTM The actual query I've done was: select s.* from sales_unit s left join sales_unit_relation r on (s.sales_unit_id = r.sales_unit_child_id) where r.sales_unit_child_id is null select * from sales_unit s left join sales_unit_relation r on (s.sales_unit_id = r.sales_unit_child_id) where r.sales_unit_child_id is null Same query, both uses left join and only difference is with select.

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• HTML prevent line break (between two table tags)

  - by arik-so

  Hello, I have following code: <table> <tr> <td>Table 1</td> </tr> </table> <table> <tr> <td>Table 2</td> </tr> </table> Very unfortunately, a line break is inserted between these two tables. I have tried putting them both in a single span and setting the whitespace to nowrap, but at no avail. Please, could you tell me how I can simply put these elements in a single row, without setting the float attribute in CSS and without surrounding each table with a <td> {table} </td> and then putting this in a table row. Thanks a lot in advance. I have asked Google, but it just wouldn't say anything ^^ StackOverflow remained silent so far, too

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• Consecutive absences in MySQL

  - by pepersview

  Hi, I have 2 tables in my db: students and absences. In students: id_student, s_name; and in absences: id_student, date, day(the day of the week as number-it's not so important); I would like to get the students that were absent for more than 2 days consecutive and the dates. At the moment I have the next query: /*To control when the days are in the same week*/ SELECT id_student, date, dayname(date),date_add(date, INTERVAL 1 DAY) AS a, dayname(date_add(date, INTERVAL 1 DAY)) AS an, date_add(date, INTERVAL 2 DAY) AS b, dayname(date_add(date, INTERVAL 2 DAY)) AS bn FROM absences AS a WHERE id_student IN (SELECT id_student FROM absences WHERE id_student = a.id_student AND date = date_add(a.date, INTERVAL 1 DAY) ) AND id_student IN (SELECT id_student FROM absences WHERE id_student = a.id_student AND date = date_add(a.date,INTERVAL 2 DAY) ) UNION /*To control when the days jump to the next week*/ SELECT id_student, date, dayname(date),date_add(date, INTERVAL 3 DAY) AS a, dayname(date_add(date, INTERVAL 3 DAY)) AS an, date_add(date, INTERVAL 4 DAY) AS b, dayname(date_add(date, INTERVAL 4 DAY)) AS bn FROM absences AS a WHERE id_student IN (SELECT id_student FROM absences WHERE id_student = a.id_student AND date = date_add(a.date, INTERVAL 3 DAY) ) AND id_student IN (SELECT id_student FROM absences WHERE id_student = a.id_student AND date = date_add(a.date,INTERVAL 4 DAY) ) /* To avoid the case (Monday-Thursday-Friday) to be consider as consecutive days*/ AND WEEKDAY(date) !=0 Thanks

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• Storing Number in an integer from sql Database

  - by ar31an

  i am using database with table RESUME and column PageIndex in it which type is number in database but when i want to store this PageIndex value to an integer i get exception error Specified cast is not valid. here is the code string sql; string conString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=D:\\Deliverable4.accdb"; protected OleDbConnection rMSConnection; protected OleDbDataAdapter rMSDataAdapter; protected DataSet dataSet; protected DataTable dataTable; protected DataRow dataRow; on Button Click sql = "select PageIndex from RESUME"; rMSConnection = new OleDbConnection(conString); rMSDataAdapter = new OleDbDataAdapter(sql, rMSConnection); dataSet = new DataSet("pInDex"); rMSDataAdapter.Fill(dataSet, "RESUME"); dataTable = dataSet.Tables["RESUME"]; int pIndex = (int)dataTable.Rows[0][0]; rMSConnection.Close(); if (pIndex == 0) { Response.Redirect("Create Resume-1.aspx"); } else if (pIndex == 1) { Response.Redirect("Create Resume-2.aspx"); } else if (pIndex == 2) { Response.Redirect("Create Resume-3.aspx"); } } i am getting error in this line int pIndex = (int)dataTable.Rows[0][0];

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• Is it possible to aggregate over differing where clauses?

  - by BenAlabaster

  Is it possible to calculate multiple aggregates based on differing where clauses? For instance: Let's say I have two tables, one for Invoice and one for InvoiceLineItems. The invoice table has a total field for the invoice total, and each of the invoice line item records in the InvoiceLineItems table contains a field that denotes whether the line item is discountable or not. I want three sum totals, one where Discountable = 0 and one where Discountable = 1 and one where Discountable is irrelevant. Such that my output would be: InvoiceNumber Total DiscountableTotal NonDiscountableTotal ------------- ----- ----------------- -------------------- 1 53.27 27.27 16.00 2 38.94 4.76 34.18 3... The only way I've found so far is by using something like: Select i.InvoiceNumber, i.Total, t0.Total As DiscountableTotal, t1.Total As NonDiscountableTotal From Invoices i Left Join ( Select InvoiceNumber, Sum(Amount), From InvoiceLineItems Where Discountable = 0 Group By InvoiceNumber ) As t0 On i.InvoiceNumber = t0.InvoiceNumber Left Join ( Select InvoiceNumber, Sum(Amount) From InvoiceLineItems Where Discountable = 1 Group By InvoiceNumber ) As t1 On i.InvoiceNumber = t1.InvoiceNumber This seems somewhat cumbersome, it would be nice if I could do something like: Select InvoiceNumber, Sum(Amount) Where Discountable = 1 As Discountable Sum(Amount) Where Discountable = 0 As NonDiscountable Group By InvoiceNumber I realize that SQL is completely invalid, but it logically portrays what I'm trying to do... TIA P.S. I need this to run on a SQL Server 2000 instance, but I am also interested (for future reference) if/how I would achieve this on SQL Server 2005/2008.

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• How to handle ids and polymorphic associations in views if compound keys are not supported?

  - by duncan

  I have a Movie plan table: movie_plans (id, description) Each plan has items, which describe a sequence of movies and the duration in minutes: movie_plan_items (id, movie_plan_id, movie_id, start_minutes, end_minutes) A specific instance of that plan happens in: movie_schedules (id, movie_plan_id, start_at) However the schedule items can be calculated from the movie_plan_items and the schedule start time by adding the minutes create view movie_schedule_items as select CONCAT(p.id, '-', s.id) as id, s.id as movie_schedule_id, p.id as movie_plan_item_id, p.movie_id, p.movie_plan_id, (s.start_at + INTERVAL p.start_minutes MINUTE) as start_at, (s.start_at + INTERVAL p.end_minutes MINUTE) as end_at from movie_plan_items p, movie_schedules s where s.movie_plan_id=p.movie_plan_id; I have a model over this view (readonly), it works ok, except that the id is right now a string. I now want to add a polymorphic property (like comments) to various of the previous tables. Therefore for movie_schedule_items I need a unique and persistent numeric id. I have the following dilemma: I could avoid the id and have movie_schedule_items just use the movie_plan_id and movie_schedule_id as a compound key, as it should. But Rails sucks in this regard. I could create an id using String#hash or a md5, thus making it slower or collision prone (and IIRC String#hash is no longer persistent across processes in Ruby 1.9) Any ideas on how to handle this situation?

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• Why can't we just use a hash of passphrase as the encryption key (and IV) with symmetric encryption algorithms?

  - by TX_

  Inspired by my previous question, now I have a very interesting idea: Do you really ever need to use Rfc2898DeriveBytes or similar classes to "securely derive" the encryption key and initialization vector from the passphrase string, or will just a simple hash of that string work equally well as a key/IV, when encrypting the data with symmetric algorithm (e.g. AES, DES, etc.)? I see tons of AES encryption code snippets, where Rfc2898DeriveBytes class is used to derive the encryption key and initialization vector (IV) from the password string. It is assumed that one should use a random salt and a shitload of iterations to derive secure enough key/IV for the encryption. While deriving bytes from password string using this method is quite useful in some scenarios, I think that's not applicable when encrypting data with symmetric algorithms! Here is why: using salt makes sense when there is a possibility to build precalculated rainbow tables, and when attacker gets his hands on hash he looks up the original password as a result. But... with symmetric data encryption, I think this is not required, as the hash of password string, or the encryption key, is never stored anywhere. So, if we just get the SHA1 hash of password, and use it as the encryption key/IV, isn't that going to be equally secure? What is the purpose of using Rfc2898DeriveBytes class to generate key/IV from password string (which is a very very performance-intensive operation), when we could just use a SHA1 (or any other) hash of that password? Hash would result in random bit distribution in a key (as opposed to using string bytes directly). And attacker would have to brute-force the whole range of key (e.g. if key length is 256bit he would have to try 2^256 combinations) anyway. So either I'm wrong in a dangerous way, or all those samples of AES encryption (including many upvoted answers here at SO), etc. that use Rfc2898DeriveBytes method to generate encryption key and IV are just wrong.

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• Designing a database for a user/points system? (in Django)

  - by AP257

  First of all, sorry if this isn't an appropriate question for StackOverflow. I've tried to make it as generalisable as possible. I want to create a database (MySQL, site running Django) that has users, who can be allocated a certain number of points for various types of action - it's a collaborative game. My requirements are to obtain: the number of points a user has the user's ranking compared to all other users and the overall leaderboard (i.e. all users ranked in order of points) This is what I have so far, in my Django models.py file: class SiteUser(models.Model): name = models.CharField(max_length=250 ) email = models.EmailField(max_length=250 ) date_added = models.DateTimeField(auto_now_add=True) def points_total(self): points_added = PointsAdded.objects.filter(user=self) points_total = 0 for point in points_added: points_total += point.points return points_total class PointsAdded(models.Model): user = models.ForeignKey('SiteUser') action = models.ForeignKey('Action') date_added = models.DateTimeField(auto_now_add=True) def points(self): points = Action.objects.filter(action=self.action) return points class Action(models.Model): points = models.IntegerField() action = models.CharField(max_length=36) However it's rapidly becoming clear to me that it's actually quite complex (in Django query terms at least) to figure out the user's ranking and return the leaderboard of users. At least, I'm finding it tough. Is there a more elegant way to do something like this? This question seems to suggest that I shouldn't even have a separate points table - what do people think? It feels more robust to have separate tables, but I don't have much experience of database design.

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• How to document an existing small web site (web application), inside and out?

  - by Ricket

  We have a "web application" which has been developed over the past 7 months. The problem is, it was not really documented. The requirements consisted of a small bulleted list from the initial meeting 7 months ago (it's more of a "goals" statement than software requirements). It has collected a number of features which stemmed from small verbal or chat discussions. The developer is leaving very soon. He wrote the entire thing himself and he knows all of the quirks and underlying rules to each page, but nobody else really knows much more than the user interface side of it; which of course is the easy part, as it's made to be intuitive to the user. But if someone needs to repair or add a feature to it, the entire thing is a black box. The code has some minimal comments, and of course the good thing about web applications is that the address bar points you in the right direction towards fixing a problem or upgrading a page. But how should the developer go about documenting this web application? He is a bit lost as far as where to begin. As developers, how do you completely document your web applications for other developers, maintainers, and administrative-level users? What approach do you use, where do you start, do you have a template? An idea of magnitude: it uses PHP, MySQL and jQuery. It has about 20-30 main (frontend) files, along with about 15 included files and a couple folders of some assets. So overall it's a pretty small application. It interfaces with 7 MySQL tables, each one well-named, so I think the database end is pretty self-explanatory. There is a config.inc.php file with definitions of consts like the MySQL user details, some from/to emails, and URLs which PHP uses to insert into emails and pages (relative and absolute paths, basiecally). There is some AJAX via jQuery. Please comment if there is any other information that would help you help me and I will be glad to edit it in.

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• Oracle Query Optimization: Why is My Second Query Faster?

  - by Patrick Cuff

  I was having some performance issues with an Oracle query, so I downloaded a trial of the Quest SQL Optimizer for Oracle, which made some changes that dramatically improved the query's performance. I'm not exactly sure why the recommended query had such an improvement; can anyone provide an explanation? Before: SELECT t1.version_id, t1.id, t2.field1, t3.person_id, t2.id FROM table1 t1, table2 t2, table3 t3 WHERE t1.id = t2.id AND t1.version_id = t2.version_id AND t2.id = 123 AND t1.version_id = t3.version_id AND t1.VERSION_NAME <> 'AA' order by t1.id Plan Cost: 831 Elapsed Time: 00:00:21.40 Number of Records: 40,717 After: SELECT /*+ USE_NL_WITH_INDEX(t1) */ t1.version_id, t1.id, t2.field1, t3.person_id, t2.id FROM table2 t2, table3 t3, table1 t1 WHERE t1.id = t2.id + 0 AND t1.version_id = t2.version_id + 0 AND t2.id = 123 AND t1.version_id = t3.version_id + 0 AND t1.VERSION_NAME || '' <> 'AA' AND t3.version_id = t2.version_id + 0 order by t1.id Plan Cost: 686 Elapsed Time: 00:00:00.95 Number of Records: 40,717 Questions: Why does re-arranging the order of the tables in the FROM clause help? Why does adding + 0 to the WHERE clause comparisons help? Why does || '' <> 'AA' in the WHERE clause VERSION_NAME comparison help? Is this a more efficient way of handling possible nulls on this column?

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