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• For a set of sql-queries, how do you determine which result-set contains a certain row?

  - by ManBugra

  I have a set of sql - queries: List<String> queries = ... queries[0] = "select id from person where ..."; ... queries[8756] = "select id from person where ..."; Each query selects rows from the same table 'person'. The only difference is the where-clause. Table 'person' looks like this: id | name | ... many other columns How can i determine which queries will contain a certain person in their subset? For example: List<Integer> matchingQueries = magicMethod(queries, [23,45]); The list obtained by 'magicMethod' filters all sql queries present in the list 'queries' (defined above) and returns only those that contain either the person with id 23 OR a person with id 45. Why i need it: I am dealing with an application that contains products and categories where the categories are sql queries that define which products belong to them (queries stored in a table also). Now i have a requirement where an admin has to see all categories an item belongs to immediately after the item was created. Btw, over 8.000 categories defined (so far, more to come). language and db: java && postgreSQL Thanks,

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• Do you like languages that let you put the "then" before the "if"?

  - by Matt Hamilton

  I was reading through some C# code of mine today and found this line: if (ProgenyList.ItemContainerGenerator.Status != System.Windows.Controls.Primitives.GeneratorStatus.ContainersGenerated) return; Notice that you can tell without scrolling that it's an "if" statement that works with ItemContainerGenerator.Status, but you can't easily tell that if the "if" clause evaluates to "false" the method will return at that point. Realistically I should have moved the "return" statement to a line by itself, but it got me thinking about languages that allow the "then" part of the statement first. If C# permitted it, the line could look like this: return if (ProgenyList.ItemContainerGenerator.Status != System.Windows.Controls.Primitives.GeneratorStatus.ContainersGenerated); This might be a bit "argumentative", but I'm wondering what people think about this kind of construct. It might serve to make lines like the one above more readable, but it also might be disastrous. Imagine this code: return 3 if (x > y); Logically we can only return if x y, because there's no "else", but part of me looks at that and thinks, "are we still returning if x <= y? If so, what are we returning?" What do you think of the "then before the if" construct? Does it exist in your language of choice? Do you use it often? Would C# benefit from it?

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• Can't get jQuery to wokr with Prototype - tried everything....

  - by thinkfuture

  Ok so here is the situation. Been pulling my hair out on this one. I'm a noob at this. Only been using rails for about 6 weeks. I'm using the standard setup package, and my code leverages prototype helpers heavily. Like I said, noob ;) So I'm trying to put in some jQuery effects, like PrettyPhoto. But what happens is that when the page is first loaded, PrettyPhoto works great. However, once someone uses a Prototype helper, like a link created with link_to_remote, Prettyphoto stops working. I've tried jRails, all of the fixes proposed on the JQuery site to stop conflicts... http://docs.jquery.com/Using_jQuery_with_Other_Libraries ...even done some crazy things likes renaming all of the $ in prototype.js to $$$ to no avail. Either the prototype helpers break, or jQuery breaks. Seems nothing I do can get these to work together. Any ideas? Here is part of my application.html.erb <%= javascript_include_tag 'application' %> <%= javascript_include_tag 'tooltip' %> <%= javascript_include_tag 'jquery' %> <%= javascript_include_tag 'jquery-ui' %> <%= javascript_include_tag "jquery.prettyPhoto" %> <%= javascript_include_tag 'prototype' %> <%= javascript_include_tag 'scriptalicious' %> </head> <body> <script type="text/javascript" charset="utf-8"> jQuery(document).ready( function() { jQuery("a[rel^='prettyPhoto']").prettyPhoto(); }); </script> If I put prototype before jquery, the prototype helpers don't work If I put the noconflict clause in, neither works. Thanks in advance! Chris

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• How to return a record from function executed by INSERT/UPDATE rule?

  - by seas

  Do the following scheme for my database: create sequence data_sequence; create table data_table { id integer primary key; field varchar(100); }; create view data_view as select id, field from data_table; create function data_insert(_new data_view) returns data_view as $$declare _id integer; _result data_view%rowtype; begin _id := nextval('data_sequence'); insert into data_table(id, field) values(_id, _new.field); select * into _result from data_view where id = _id; return _result; end; $$ language plpgsql; create rule insert as on insert to data_view do instead select data_insert(new); Then type in psql: insert into data_view(field) values('abc'); Would like to see something like: id | field ----+--------- 1 | abc Instead see: data_insert ------------- (1, "abc") Is it possible to fix this somehow? Thanks for any ideas. Ultimate idea is to use this in other functions, so that I could obtain id of just inserted record without selecting for it from scratch. Something like: insert into data_view(field) values('abc') returning id into my_variable would be nice but doesn't work with error: ERROR: cannot perform INSERT RETURNING on relation "data_view" HINT: You need an unconditional ON INSERT DO INSTEAD rule with a RETURNING clause. I don't really understand that HINT. I use PostgreSQL 8.4.

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• Connecting to SQL Server 2005 via Web Service

  - by clear-cycle-corp

  Delphi 2010, dbExpress, and SQL Server 2005 DB I am trying to make a connection to a SQL Server 2005 DB using Delphi 2010 & DBExpress. If I create a standard delphi application and hard code my connection (IT WORKS!): procedure TForm1.Button1Click(Sender: TObject); var Conn: TSQLConnection; begin Conn:= TSQLConnection.Create(nil); Conn.ConnectionName:= 'VPUCDS_VPN_SE01'; Conn.LoadParamsOnConnect := True; Conn.LoginPrompt:=True; try Conn.Connected:= True; if Conn.Connected then ShowMessage('Connected!') else ShowMessage('NOT Connected!') finally Conn.Free; end; end; All the ini files, and DLLs reside in the same folder as my executable and yes, I have DBXMsSQL & MidasLib in the uses clause again, it works if its not a web service! However, if i then move the code over to a Web services CGI module: function TTest.ConnectToDB: Boolean;stdcall; var Conn: TSQLConnection; begin Conn:= TSQLConnection.Create(nil); Conn.ConnectionName:= 'VPUCDS_VPN_SE01'; Conn.LoadParamsOnConnect := True; Conn.LoginPrompt:=True; try Conn.Connected:= True; result:= Conn.Connected; finally Conn.Free; end; end; Thanks

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• Need a workaround to filter on related model and aggregated fields in Django

  - by parxier

  I opened a ticket for this problem. In a nutshell here is my model: class Plan(models.Model): cap = models.IntegerField() class Phone(models.Model): plan = models.ForeignKey(Plan, related_name='phones') class Call(models.Model): phone = models.ForeignKey(Phone, related_name='calls') cost = models.IntegerField() I want to run a query like this one: Phone.objects.annotate(total_cost=Sum('calls__cost')).filter(total_cost__gte=0.5*F('plan__cap')) Unfortunately Django generates bad SQL: SELECT "app_phone"."id", "app_phone"."plan_id", SUM("app_call"."cost") AS "total_cost" FROM "app_phone" INNER JOIN "app_plan" ON ("app_phone"."plan_id" = "app_plan"."id") LEFT OUTER JOIN "app_call" ON ("app_phone"."id" = "app_call"."phone_id") GROUP BY "app_phone"."id", "app_phone"."plan_id" HAVING SUM("app_call"."cost") >= 0.5 * "app_plan"."cap" and errors with: ProgrammingError: column "app_plan.cap" must appear in the GROUP BY clause or be used in an aggregate function LINE 1: ...."plan_id" HAVING SUM("app_call"."cost") >= 0.5 * "app_plan".... Is there any workaround apart from running raw SQL?

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• How to return a record from function, executed by INSERT/UPDATE rule (trigger)?

  - by seas

  Do the following scheme for my database: create sequence data_sequence; create table data_table { id integer primary key; field varchar(100); }; create view data_view as select id, field from data_table; create function data_insert(_new data_view) returns data_view as $$declare _id integer; _result data_view%rowtype; begin _id := nextval('data_sequence'); insert into data_table(id, field) values(_id, _new.field); select * into _result from data_view where id = _id; return _result; end; $$ language plpgsql; create rule insert as on insert to data_view do instead select data_insert(new); Then type in psql: insert into data_view(field) values('abc'); Would like to see something like: id | field ----+--------- 1 | abc Instead see: data_insert ------------- (1, "abc") Is it possible to fix this somehow? Thanks for any ideas. Ultimate idea is to use this in other functions, so that I could obtain id of just inserted record without selecting for it from scratch. Something like: insert into data_view(field) values('abc') returning id into my_variable would be nice but doesn't work with error: ERROR: cannot perform INSERT RETURNING on relation "data_view" HINT: You need an unconditional ON INSERT DO INSTEAD rule with a RETURNING clause. I don't really understand that HINT. I use PostgreSQL 8.4.

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• SQL n:m Inheritance join

  - by Nightmares

  I want to join a table which contains n:m relationship between groups. (Groups are defined in a separate table). This table only has entries listing a member_group_id and a parent_group_id. Given this structure: id(int) | member_group_id(int) | parent_group_id(int) The "base" query looks like this: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.member_group_id = p1.member_group_id The "base" query correctly shows all relationships (I checked by doing it manually.) The problem is when I try to apply a where clause to this query to filter for a specific group as "point of origin" (the first group for which I want all parent groups) it returns only the closest parents. For example like this: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.member_group_id = p1.member_group_id where p1.group_id = 1 Can anyone give a clue how I can fix this? Or a different approach to realize this. (I suppose I could always do this in my C++ source code on the server side but I would have to transfer a entire table which has a high growth potential to the application server.) UPDATE: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.group_id = p1.member_group_id Typing mistake confirmed. Now I don't get past first level of inheritance period. Thanks at denied for pointing that out.

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• Interesting LinqToSql behaviour

  - by Ben Robinson

  We have a database table that stores the location of some wave files plus related meta data. There is a foreign key (employeeid) on the table that links to an employee table. However not all wav files relate to an employee, for these records employeeid is null. We are using LinqToSQl to access the database, the query to pull out all non employee related wav file records is as follows: var results = from Wavs in db.WaveFiles where Wavs.employeeid == null; Except this returns no records, despite the fact that there are records where employeeid is null. On profiling sql server i discovered the reason no records are returned is because LinqToSQl is turning it into SQL that looks very much like: SELECT Field1, Field2 //etc FROM WaveFiles WHERE 1=0 Obviously this returns no rows. However if I go into the DBML designer and remove the association and save. All of a sudden the exact same LINQ query turns into SELECT Field1, Field2 //etc FROM WaveFiles WHERE EmployeeID IS NULL I.e. if there is an association then LinqToSql assumes that all records have a value for the foreign key (even though it is nullable and the property appears as a nullable int on the WaveFile entity) and as such deliverately constructs a where clause that will return no records. Does anyone know if there is a way to keep the association in LinqToSQL but stop this behaviour. A workaround i can think of quickly is to have a calculated field called IsSystemFile and set it to 1 if employeeid is null and 0 otherwise. However this seems like a bit of a hack to work around strange behaviour of LinqToSQl and i would rather do something in the DBML file or define something on the foreign key constraint that will prevent this behaviour.

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• Linq generic Expression in query on "element" or on IQueryable (multiple use)

  - by Bogdan Maxim

  Hi, I have the following expression public static Expression<Func<T, bool>> JoinByDateCheck<T>(T entity, DateTime dateToCheck) where T : IDateInterval { return (entityToJoin) => entityToJoin.FromDate.Date <= dateToCheck.Date && (entityToJoin.ToDate == null || entityToJoin.ToDate.Value.Date >= dateToCheck.Date); } IDateInterval interface is defined like this: interface IDateInterval { DateTime FromDate {get;} DateTime? ToDate {get;} } and i need to apply it in a few ways: (1) Query on Linq2Sql Table: var q1 = from e in intervalTable where FunctionThatCallsJoinByDateCheck(e, constantDateTime) select e; or something like this: intervalTable.Where(FunctionThatCallsJoinByDateCheck(e, constantDateTime)) (2) I need to use it in some table joins (as linq2sql doesn't provide comparative join): var q2 = from e1 in t1 join e2 in t2 on e1.FK == e2.PK where OtherFunctionThatCallsJoinByDateCheck(e2, e1.FromDate) or var q2 = from e1 in t1 from e2 in t2 where e1.FK == e2.PK && OtherFunctionThatCallsJoinByDateCheck(e2, e1.FromDate) (3) I need to use it in some queries like this: var q3 = from e in intervalTable.FilterFunctionThatCallsJoinByDateCheck(constantDate); Dynamic linq is not something that I can use, so I have to stick to plain linq. Thank you Clarification: Initially I had just the last method (FilterFunctionThatCallsJoinByDateCheck(this IQueryable<IDateInterval> entities, DateTime dateConstant) ) that contained the code from the expression. The problem is that I get a SQL Translate exception if I write the code in a method and call it like that. All I want is to extend the use of this function to the where clause (see the second query in point 2)

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• Conditional insert as a single database transaction in HSQLDB 1.8?

  - by Kevin Pauli

  I'm using a particular database table like a "Set" data structure, i.e., you can attempt to insert the same row several times, but it will only contain one instance. The primary key is a natural key. For example, I want the following series of operations to work fine, and result in only one row for Oklahoma: insert into states_visited (state_name) values ('Oklahoma'); insert into states_visited (state_name) values ('Texas'); insert into states_visited (state_name) values ('Oklahoma'); I am of course getting an error due to the duplicate primary key on subsequent inserts of the same value. Is there a way to make the insert conditional, so that these errors are not thrown? I.e. only do the the insert if the natural key does not already exist? I know I could do a where clause and a subquery to test for the row's existence first, but it seems that would be expensive. That's 2 physical operations for one logical "conditional insert" operation. Anything like this in SQL? FYI I am using HSQLDB 1.8

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• MFC/CCriticalSection: Simple lock situation hangs

  - by raph.amiard

  I have to program a simple threaded program with MFC/C++ for a uni assignment. I have a simple scenario in wich i have a worked thread which executes a function along the lines of : UINT createSchedules(LPVOID param) { genProgThreadVal* v = (genProgThreadVal*) param; // v->searcherLock is of type CcriticalSection* while(1) { if(v->searcherLock->Lock()) { //do the stuff, access shared object , exit clause etc.. v->searcherLock->Unlock(); } } PostMessage(v->hwnd, WM_USER_THREAD_FINISHED , 0,0); delete v; return 0; } In my main UI class, i have a CListControl that i want to be able to access the shared object (of type std::List). Hence the locking stuff. So this CList has an handler function looking like this : void Ccreationprogramme::OnLvnItemchangedList5(NMHDR *pNMHDR, LRESULT *pResult) { LPNMLISTVIEW pNMLV = reinterpret_cast<LPNMLISTVIEW>(pNMHDR); if((pNMLV->uChanged & LVIF_STATE) && (pNMLV->uNewState & LVNI_SELECTED)) { searcherLock.Lock(); // do the stuff on shared object searcherLock.Unlock(); // do some more stuff } *pResult = 0; } The searcherLock in both function is the same object. The worker thread function is passed a pointer to the CCriticalSection object, which is a member of my dialog class. Everything works but, as soon as i do click on my list, and so triggers the handler function, the whole program hangs indefinitely.I tried using a Cmutex. I tried using a CSingleLock wrapping over the critical section object, and none of this has worked. What am i missing ?

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• NullPointerException on Activity Testing Tutorial

  - by Bendik

  Hello, I am currently trying the activity testing tutorial (Found here), and have a problem. It seems that whenever I try to call something inside the UIThread, I get a java.lang.NullPointerException. public void testSpinnerUI() { mActivity.runOnUiThread( new Runnable() { public void run() { mSpinner.requestFocus(); } }); } This gives me: Incomplete: java.lang.NullPointerException and nothing else. I have tried this on two different samples now, with the same result. I tried with a try/catch clause around the mSpinner.requestFocus() call, and it seems that mSpinner is null inside the thread. I have set it properly up with the setUp() function found in the same sample, and a quick assertNotNull( mSpinner ) shows me that mSpinner is in fact not null after the setUp() function. What can be the cause of this? EDIT; ok, some more testing has been done. It seems that the application that is being tested resets between each test. This essentially makes me have to reinstantiate all variables between each test. Is this normal?

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• Excessive use of Inner Join for more than 3 tables

  - by Archangel08

  Good Day, I have 4 tables on my DB (not the actual name but almost similar) which are the ff: employee,education,employment_history,referrence employee_id is the name of the foreign key from employee table. Here's the example (not actual) data: **Employee** ID Name Birthday Gender Email 1 John Smith 08-15-2014 Male [email protected] 2 Jane Doe 00-00-0000 Female [email protected] 3 John Doe 00-00-0000 Male [email protected] **Education** Employee_ID Primary Secondary Vocation 1 Westside School Westshore H.S SouthernBay College 2 Eastside School Eastshore H.S NorthernBay College 3 Northern School SouthernShore H.S WesternBay College **Employment_History** Employee_ID WorkOne StartDate Enddate 1 StarBean Cafe 12-31-2012 01-01-2013 2 Coffebucks Cafe 11-01-2012 11-02-2012 3 Latte Cafe 01-02-2013 04-05-2013 Referrence Employee_ID ReferrenceOne Address Contact 1 Abraham Lincoln Lincoln Memorial 0000000000 2 Frankie N. Stein Thunder St. 0000000000 3 Peter D. Pan Neverland Ave. 0000000000 NOTE: I've only included few columns though the rest are part of the query. And below are the codes I've been working on for 3 consecutive days: $sql=mysql_query("SELECT emp.id,emp.name,emp.birthday,emp.pob,emp.gender,emp.civil,emp.email,emp.contact,emp.address,emp.paddress,emp.citizenship,educ.employee_id,educ.elementary,educ.egrad,educ.highschool,educ.hgrad,educ.vocational,educ.vgrad,ems.employee_id,ems.workOne,ems.estartDate,ems.eendDate,ems.workTwo,ems.wstartDate,ems.wendDate,ems.workThree,ems.hstartDate,ems.hendDate FROM employee AS emp INNER JOIN education AS educ ON educ.employee_id='emp.id' INNER JOIN employment_history AS ems ON ems.employee_id='emp.id' INNER JOIN referrence AS ref ON ref.employee_id='emp.id' WHERE emp.id='$id'"); Is it okay to use INNER JOIN this way? Or should I modify my query to get the results that I wanted? I've also tried to use LEFT JOIN but still it doesn't return anything .I didn't know where did I go wrong. You see, as I have thought, I've been using the INNER JOIN in correct manner, (since it was placed before the WHILE CLAUSE). So I couldn't think of what could've possible went wrong. Do you guys have a suggestion? Thanks in advance.

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• Learn Prolog Now! DCG Practice Example

  - by Timothy

  I have been progressing through Learn Prolog Now! as self-study and am now learning about Definite Clause Grammars. I am having some difficulty with one of the Practical Session's tasks. The task reads: The formal language anb2mc2mdn consists of all strings of the following form: an unbroken block of as followed by an unbroken block of bs followed by an unbroken block of cs followed by an unbroken block of ds, such that the a and d blocks are exactly the same length, and the c and d blocks are also exactly the same length and furthermore consist of an even number of cs and ds respectively. For example, ε, abbccd, and aaabbbbccccddd all belong to anb2mc2mdn. Write a DCG that generates this language. I am able to write rules that generate andn, b2mc2m, and even anb2m and c2mndn... but I can't seem to join all these rules into anb2mc2mdn. The following are my rules that can generate andn and b2mc2m. s1 --> []. s1 --> a,s1,d. a --> [a]. d --> [d]. s2 --> []. s2 --> c,c,s2,d,d. c --> [c]. d --> [d]. Is anb2mc2mdn really a CFG, and is it possible to write a DCG using only what was taught in the lesson (no additional arguments or code, etc)? If so, can anyone offer me some guidance how I can join these so that I can solve the given task?

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• Simple POSIX threads question

  - by Andy

  Hi, I have this POSIX thread: void subthread(void) { while(!quit_thread) { // do something ... // don't waste cpu cycles if(!quit_thread) usleep(500); } // free resources ... // tell main thread we're done quit_thread = FALSE; } Now I want to terminate subthread() from my main thread. I've tried the following: quit_thread = TRUE; // wait until subthread() has cleaned its resources while(quit_thread); But it does not work! The while() clause does never exit although my subthread clearly sets quit_thread to FALSE after having freed its resources! If I modify my shutdown code like this: quit_thread = TRUE; // wait until subthread() has cleaned its resources while(quit_thread) usleep(10); Then everything is working fine! Could someone explain to me why the first solution does not work and why the version with usleep(10) suddenly works? I know that this is not a pretty solution. I could use semaphores/signals for this but I'd like to learn something about multithreading, so I'd like to know why my first solution doesn't work. Thanks!

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• .NET Error with Dynamic T-SQL

  - by Phillip Theriault

  I am trying to create a TableAdapter in .NET using a stored procedure, but I'm getting an error "Incorrect syntax near the keyword 'WHERE'". I have narrowed down the problem in the stored procedure to the following lines: IF @NumRows > 0 SET @SQL += N' WHERE T1.RowNumber BETWEEN 1 and 10' ELSE SET @SQL += N' WHERE T1.RowNumber > 0' @NumRows is an input parameter that defaults to 0. However, if I remove either of those lines everything works fine (both WHERE clauses work fine by themselves when there is no IF/ELSE statement). It almost looks like .NET is ignoring the IF/ELSE and attempting to add the WHERE clause twice. It also works fine if I change it like so: IF @NumRows > 0 SET @SQL += N'' ELSE SET @SQL += N' WHERE T1.RowNumber > 0' One of the WHERE clauses has been removed, and there's no longer a conflict on the .NET side. So I'm pretty sure it has to do with the 2 WHERE clauses, and not with anything else. The sproc runs perfectly fine in SQL Server, and it even runs in .NET despite the error if I click "Preview Data". The only problem is that it won't auto-populate the list of fields, which I need for creating a report. Has anybody seen this before and have a suggestion?

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• MySQL to PostreSQL and Named Scope

  - by Lowgain

  I've got a named scope for one of my models that works fine. The code is: named_scope :inbox_threads, lambda { |user| { :include => [:deletion_flags, :recipiences], :conditions => ["recipiences.user_id = ? AND deletion_flags.user_id IS NULL", user.id], :group => "msg_threads.id" }} This works fine on my local copy of the app with a MySQL database, but when I push my app to Heroku (which only uses PostgreSQL), I get the following error: ActiveRecord::StatementInvalid (PGError: ERROR: column "msg_threads.subject" must appear in the GROUP BY clause or be used in an aggregate function: SELECT "msg_threads"."id" AS t0_r0, "msg_threads"."subject" AS t0_r1, "msg_threads"."originator_id" AS t0_r2, "msg_thr eads"."created_at" AS t0_r3, "msg_threads"."updated_at" AS t0_r4, "msg_threads"."url_key" AS t0_r5, "deletion_flags"."id" AS t1_r0, "deletion_flags"."user_id" AS t1_r1, "deletion_flags"."msg_thread_id" AS t1_r2, "deletion_flags"."confirmed" AS t1_r3, "deletion_flags"."created_at" AS t1_r4, "deletion_flags"."updated_at" AS t1_r5, "recipiences"."id" AS t2_r0, "recipiences"."user_id" AS t2_r1, "recipiences"."msg_thread_id" AS t2_r2, "recipiences"."created_at" AS t2_r3, "recipien ces"."updated_at" AS t2_r4 FROM "msg_threads" LEFT OUTER JOIN "deletion_flags" ON deletion_flags.msg_thread_id = msg_threads.id LEFT OUTER JOIN "recipiences" ON recipiences.msg_thread_id = msg_threads.id WHERE (recipiences.user_id = 1 AND deletion_flags.user_id IS NULL) GROUP BY msg_threads.id) I'm not as familiar with the working of Postgres, so what would I need to add here to get this working? Thanks!

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• Queries within queries: Is there a better way?

  - by mririgo

  As I build bigger, more advanced web applications, I'm finding myself writing extremely long and complex queries. I tend to write queries within queries a lot because I feel making one call to the database from PHP is better than making several and correlating the data. However, anyone who knows anything about SQL knows about JOINs. Personally, I've used a JOIN or two before, but quickly stopped when I discovered using subqueries because it felt easier and quicker for me to write and maintain. Commonly, I'll do subqueries that may contain one or more subqueries from relative tables. Consider this example: SELECT (SELECT username FROM users WHERE records.user_id = user_id) AS username, (SELECT last_name||', '||first_name FROM users WHERE records.user_id = user_id) AS name, in_timestamp, out_timestamp FROM records ORDER BY in_timestamp Rarely, I'll do subqueries after the WHERE clause. Consider this example: SELECT user_id, (SELECT name FROM organizations WHERE (SELECT organization FROM locations WHERE records.location = location_id) = organization_id) AS organization_name FROM records ORDER BY in_timestamp In these two cases, would I see any sort of improvement if I decided to rewrite the queries using a JOIN? As more of a blanket question, what are the advantages/disadvantages of using subqueries or a JOIN? Is one way more correct or accepted than the other?

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• Is there a definitive reference document for Ruby syntax?

  - by JSW

  I'm searching for a definitive document on Ruby syntax. I know about the definitive documents for the core API and standard library, but what about the syntax itself? For instance, such a document should cover: reserved words, string literals syntax, naming rules for variables/classes/modules, all the conditional statements and their permutations, and so forth. I know there are many books and tutorials, yes, but every one of them is essentially a tutorial, each one having a range of different depth and focus. They will all, by necessity of brevity and narrative flow, omit certain details of the language that the author deems insignificant. For instance, did you know that you can use a case statement without an initial case value, and it will then execute the first true when clause? Any given Ruby book or tutorial may or may not cover that particular lesser-known functionality of the case syntax. It's not discussed in the section in "Programming Ruby" about case statements. But that is just one small example. So far the best documentation I've found is the rubyspec project, which appears to be an attempt to write a complete test suite for the language. That's not bad, but it's a bit hard to use from a practical standpoint as a developer working on my own projects. Am I just missing something or is there really no definitive readable document defining the whole of Ruby syntax?

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• How to keep the CPU usage down while running an SDL program?

  - by budwiser

  I've done a very basic window with SDL and want to keep it running until I press the X on window. #include "SDL.h" const int SCREEN_WIDTH = 640; const int SCREEN_HEIGHT = 480; int main(int argc, char **argv) { SDL_Init( SDL_INIT_VIDEO ); SDL_Surface* screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, 0, SDL_HWSURFACE | SDL_DOUBLEBUF ); SDL_WM_SetCaption( "SDL Test", 0 ); SDL_Event event; bool quit = false; while (quit != false) { if (SDL_PollEvent(&event)) { if (event.type == SDL_QUIT) { quit = true; } } SDL_Delay(80); } SDL_Quit(); return 0; } I tried adding SDL_Delay() at the end of the while-clause and it worked quite well. However, 80 ms seemed to be the highest value I could use to keep the program running smoothly and even then the CPU usage is about 15-20%. Is this the best way to do this and do I have to just live with the fact that it eats this much CPU already on this point?

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• :order does not work on :include

  - by SpyrosP

  Hello there, i'm wondering why this gives me an error : DiscoveredLocation.find_all_by_user_id(user.id, :include => [:boss_location, :monsters], :order => 'boss_location.location_index ASC') It seems as if it's trying to execute a really long query and i get an error like : Mysql::Error: Unknown column 'monsters_discovered_locations_join.boss_location_id' in 'on clause': SELECT `discovered_locations`.`id` AS t0_r0, `discovered_locations`.`user_id` AS t0_r1, `discovered_locations`.`boss_location_id` AS t0_r2, `discovered_locations`.`created_at` AS t0_r3, `discovered_locations`.`updated_at` AS t0_r4, `boss_locations`.`id` AS t1_r0, `boss_locations`.`name` AS t1_r1, `boss_locations`.`location_index` AS t1_r2, `boss_locations`.`min_level` AS t1_r3, `boss_locations`.`needed_gold_to_open` AS t1_r4, `boss_locations`.`created_at` AS t1_r5, `boss_locations`.`updated_at` AS t1_r6, `monsters`.`id` AS t2_r0, `monsters`.`name` AS t2_r1, `monsters`.`strength` AS t2_r2, `monsters`.`dexterity` AS t2_r3, `monsters`.`magic` AS t2_r4, `monsters`.`accuracy` AS t2_r5, `monsters`.`minGold` AS t2_r6, `monsters`.`maxGold` AS t2_r7, `monsters`.`hp` AS t2_r8, `monsters`.`level` AS t2_r9, `monsters`.`armor` AS t2_r10, `monsters`.`first_class` AS t2_r11, `monsters`.`weapon_id` AS t2_r12, `monsters`.`imageName` AS t2_r13, `monsters`.`monster_type` AS t2_r14, `monsters`.`boss_location_index` AS t2_r15, `monsters`.`boss_location_id` AS t2_r16, `monsters`.`created_at` AS t2_r17, `monsters`.`updated_at` AS t2_r18 FROM `discovered_locations` LEFT OUTER JOIN `boss_locations` ON `boss_locations`.id = `discovered_locations`.boss_location_id LEFT OUTER JOIN `boss_locations` monsters_discovered_locations_join ON (`discovered_locations`.`id` = `monsters_discovered_locations_join`.`boss_location_id`) LEFT OUTER JOIN `monsters` ON (`monsters`.`boss_location_id` = `monsters_discovered_locations_join`.`id`) WHERE (`discovered_locations`.`user_id` = 986759322) ORDER BY boss_location.location_index ASC The models associations are : class BossKill < ActiveRecord::Base belongs_to :user belongs_to :monster class DiscoveredLocation < ActiveRecord::Base belongs_to :user belongs_to :boss_location has_many :monsters, :through => :boss_location has_many :boss_kills, :through => :monsters class BossLocation < ActiveRecord::Base has_many :discovered_locations has_many :users, :through => :discovered_locations has_many :monsters Any ideas ?

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• Mysql slow query: INNER JOIN + ORDER BY causes filesort

  - by Alexander

  Hello! I'm trying to optimize this query: SELECT `posts`.* FROM `posts` INNER JOIN `posts_tags` ON `posts`.id = `posts_tags`.post_id WHERE (((`posts_tags`.tag_id = 1))) ORDER BY posts.created_at DESC; The size of tables is 38k rows, and 31k and mysql uses "filesort" so it gets pretty slow. I tried to use different indexes, no luck. CREATE TABLE `posts` ( `id` int(11) NOT NULL auto_increment, `created_at` datetime default NULL, PRIMARY KEY (`id`), KEY `index_posts_on_created_at` (`created_at`), KEY `for_tags` (`trashed`,`published`,`clan_private`,`created_at`) ) ENGINE=InnoDB AUTO_INCREMENT=44390 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci CREATE TABLE `posts_tags` ( `id` int(11) NOT NULL auto_increment, `post_id` int(11) default NULL, `tag_id` int(11) default NULL, `created_at` datetime default NULL, `updated_at` datetime default NULL, PRIMARY KEY (`id`), KEY `index_posts_tags_on_post_id_and_tag_id` (`post_id`,`tag_id`) ) ENGINE=InnoDB AUTO_INCREMENT=63175 DEFAULT CHARSET=utf8 +----+-------------+------------+--------+--------------------------+--------------------------+---------+---------------------+-------+-----------------------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+--------+--------------------------+--------------------------+---------+---------------------+-------+-----------------------------------------------------------+ | 1 | SIMPLE | posts_tags | index | index_post_id_and_tag_id | index_post_id_and_tag_id | 10 | NULL | 24159 | Using where; Using index; Using temporary; Using filesort | | 1 | SIMPLE | posts | eq_ref | PRIMARY | PRIMARY | 4 | .posts_tags.post_id | 1 | | +----+-------------+------------+--------+--------------------------+--------------------------+---------+---------------------+-------+-----------------------------------------------------------+ 2 rows in set (0.00 sec) What kind of index I need to define to avoid mysql using filesort? Is it possible when order field is not in where clause?

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• a reusable query with modifications?

  - by fusion

  i'm using this mysql query alongwith php to search for multiple keywords: $query = "SELECT cQuotes, vAuthor, cArabic, vReference FROM ".$table." WHERE ("; $countFields = count($arrayFields); while ($a < $countFields) { while ($b < $countSearch) { $query = $query."$arrayFields[$a] LIKE '%$arraySearch[$b]%'"; $b++; if ($b < $countSearch) { $query = $query." AND "; } } $b = 0; $a++; if ($a < $countFields) { $query = $query.") OR ("; } } $query = $query.")"; $result = mysql_query($query, $conn) i'd like to reuse this query with a few modifications to it (for instance, the WHERE clause remains the same, while i query the number of rows using COUNT), but it doesn't seem practical to repeat the code again for a few additions. any suggestions?

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• querying huge database table takes too much of time in mysql

  - by Vijay

  Hi all, I am running sql queries on a mysql db table that has 110Mn+ unique records for whole day. Problem: Whenever I run any query with "where" clause it takes at least 30-40 mins. Since I want to generate most of data on the next day, I need access to whole db table. Could you please guide me to optimize / restructure the deployment model? Site description: mysql Ver 14.12 Distrib 5.0.24, for pc-linux-gnu (i686) using readline 5.0 4 GB RAM, Dual Core dual CPU 3GHz RHEL 3 my.cnf contents : [root@reports root]# cat /etc/my.cnf [mysqld] datadir=/data/mysql/data/ socket=/tmp/mysql.sock sort_buffer_size = 2000000 table_cache = 1024 key_buffer = 128M myisam_sort_buffer_size = 64M # Default to using old password format for compatibility with mysql 3.x # clients (those using the mysqlclient10 compatibility package). old_passwords=1 [mysql.server] user=mysql basedir=/data/mysql/data/ [mysqld_safe] err-log=/data/mysql/data/mysqld.log pid-file=/data/mysql/data/mysqld.pid [root@reports root]# DB table details: CREATE TABLE `RAW_LOG_20100504` ( `DT` date default NULL, `GATEWAY` varchar(15) default NULL, `USER` bigint(12) default NULL, `CACHE` varchar(12) default NULL, `TIMESTAMP` varchar(30) default NULL, `URL` varchar(60) default NULL, `VERSION` varchar(6) default NULL, `PROTOCOL` varchar(6) default NULL, `WEB_STATUS` int(5) default NULL, `BYTES_RETURNED` int(10) default NULL, `RTT` int(5) default NULL, `UA` varchar(100) default NULL, `REQ_SIZE` int(6) default NULL, `CONTENT_TYPE` varchar(50) default NULL, `CUST_TYPE` int(1) default NULL, `DEL_STATUS_DEVICE` int(1) default NULL, `IP` varchar(16) default NULL, `CP_FLAG` int(1) default NULL, `USER_LOCATE` bigint(15) default NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1 MAX_ROWS=200000000; Thanks in advance! Regards,

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