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• How much does college (e.g. a compsci major) factor into a programmer's resume? [closed]

  - by Brandon

  I was having an argument with a friend who claims that given roughly equal skill, someone with a college degree from a name school is going to start at a significantly better job (e.g. a higher-end company) for his first job; and because of this, he's also going to be significantly ahead for his second job. Here are my two questions: given equal skill, how much does college factor into a programmer's overall career? if someone has the technical skills to work competently as as programmer, is it worth it for him to go to college first? if the degree is significant, is it significant whether the degree is from an average college or a higher-tier college (e.g. Stanford, MIT)?

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• Should not a tail-recursive function also be faster?

  - by Balint Erdi

  I have the following Clojure code to calculate a number with a certain "factorable" property. (what exactly the code does is secondary). (defn factor-9 ([] (let [digits (take 9 (iterate #(inc %) 1)) nums (map (fn [x] ,(Integer. (apply str x))) (permutations digits))] (some (fn [x] (and (factor-9 x) x)) nums))) ([n] (or (= 1 (count (str n))) (and (divisible-by-length n) (factor-9 (quot n 10)))))) Now, I'm into TCO and realize that Clojure can only provide tail-recursion if explicitly told so using the recur keyword. So I've rewritten the code to do that (replacing factor-9 with recur being the only difference): (defn factor-9 ([] (let [digits (take 9 (iterate #(inc %) 1)) nums (map (fn [x] ,(Integer. (apply str x))) (permutations digits))] (some (fn [x] (and (factor-9 x) x)) nums))) ([n] (or (= 1 (count (str n))) (and (divisible-by-length n) (recur (quot n 10)))))) To my knowledge, TCO has a double benefit. The first one is that it does not use the stack as heavily as a non tail-recursive call and thus does not blow it on larger recursions. The second, I think is that consequently it's faster since it can be converted to a loop. Now, I've made a very rough benchmark and have not seen any difference between the two implementations although. Am I wrong in my second assumption or does this have something to do with running on the JVM (which does not have automatic TCO) and recur using a trick to achieve it? Thank you.

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• When to trash hashmap contents to avoid performance degradation?

  - by Jack

  Hello, I'm woking on Java with a large (millions) hashmap that is actually built with a capacity of 10.000.000 and a load factor of .75 and it's used to cache some values since cached values become useless with time (not accessed anymore) but I can't remove useless ones while on the way I would like to entirely empty the cache when its performance starts to degrade. How can I decide when it's good to do it? For example, with 10 millions capacity and .75 should I empty it when it reaches 7.5 millions of elements? Because I tried various threshold values but I would like to have an analytic one. I've already tested the fact that emping it when it's quite full is a boost for perfomance (first 2-3 algorithm iterations after the wipe just fill it back, then it starts running faster than before the wipe) Thanks

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• SQL select descendants of a row

  - by Joey Adams

  Suppose a tree structure is implemented in SQL like this: CREATE TABLE nodes ( id INTEGER PRIMARY KEY, parent INTEGER -- references nodes(id) ); Although cycles can be created in this representation, let's assume we never let that happen. The table will only store a collection of roots (records where parent is null) and their descendants. The goal is to, given an id of a node on the table, find all nodes that are descendants of it. A is a descendant of B if either A's parent is B or A's parent is a descendant of B. Note the recursive definition. Here is some sample data: INSERT INTO nodes VALUES (1, NULL); INSERT INTO nodes VALUES (2, 1); INSERT INTO nodes VALUES (3, 2); INSERT INTO nodes VALUES (4, 3); INSERT INTO nodes VALUES (5, 3); INSERT INTO nodes VALUES (6, 2); which represents: 1 `-- 2 |-- 3 | |-- 4 | `-- 5 | `-- 6 We can select the (immediate) children of 1 by doing this: SELECT a.* FROM nodes AS a WHERE parent=1; We can select the children and grandchildren of 1 by doing this: SELECT a.* FROM nodes AS a WHERE parent=1 UNION ALL SELECT b.* FROM nodes AS a, nodes AS b WHERE a.parent=1 AND b.parent=a.id; We can select the children, grandchildren, and great grandchildren of 1 by doing this: SELECT a.* FROM nodes AS a WHERE parent=1 UNION ALL SELECT b.* FROM nodes AS a, nodes AS b WHERE a.parent=1 AND b.parent=a.id UNION ALL SELECT c.* FROM nodes AS a, nodes AS b, nodes AS c WHERE a.parent=1 AND b.parent=a.id AND c.parent=b.id; How can a query be constructed that gets all descendants of node 1 rather than those at a finite depth? It seems like I would need to create a recursive query or something. I'd like to know if such a query would be possible using SQLite. However, if this type of query requires features not available in SQLite, I'm curious to know if it can be done in other SQL databases.

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• Using Recursive SQL and XML trick to PIVOT(OK, concat) a "Document Folder Structure Relationship" table, works like MySQL GROUP_CONCAT

  - by Kevin Shyr

  I'm in the process of building out a Data Warehouse and encountered this issue along the way.In the environment, there is a table that stores all the folders with the individual level.  For example, if a document is created here:{App Path}\Level 1\Level 2\Level 3\{document}, then the DocumentFolder table would look like this:IDID_ParentFolderName1NULLLevel 121Level 232Level 3To my understanding, the table was built so that:Each proposal can have multiple documents stored at various locationsDifferent users working on the proposal will have different access level to the folder; if one user is assigned access to a folder level, she/he can see all the sub folders and their content.Now we understand from an application point of view why this table was built this way.  But you can quickly see the pain this causes the report writer to show a document link on the report.  I wasn't surprised to find the report query had 5 self outer joins, which is at the mercy of nobody creating a document that is buried 6 levels deep, and not to mention the degradation in performance.With the help of 2 posts (at the end of this post), I was able to come up with this solution:Use recursive SQL to build out the folder pathUse SQL XML trick to concat the strings.Code (a reminder, I built this code in a stored procedure.  If you copy the syntax into a simple query window and execute, you'll get an incorrect syntax error) Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} -- Get all folders and group them by the original DocumentFolderID in PTSDocument table;WITH DocFoldersByDocFolderID(PTSDocumentFolderID_Original, PTSDocumentFolderID_Parent, sDocumentFolder, nLevel)AS (-- first member      SELECT 'PTSDocumentFolderID_Original' = d1.PTSDocumentFolderID            , PTSDocumentFolderID_Parent            , 'sDocumentFolder' = sName            , 'nLevel' = CONVERT(INT, 1000000)      FROM (SELECT DISTINCT PTSDocumentFolderID                  FROM dbo.PTSDocument_DY WITH(READPAST)            ) AS d1            INNER JOIN dbo.PTSDocumentFolder_DY AS df1 WITH(READPAST)                  ON d1.PTSDocumentFolderID = df1.PTSDocumentFolderID      UNION ALL      -- recursive      SELECT ddf1.PTSDocumentFolderID_Original            , df1.PTSDocumentFolderID_Parent            , 'sDocumentFolder' = df1.sName            , 'nLevel' = ddf1.nLevel - 1      FROM dbo.PTSDocumentFolder_DY AS df1 WITH(READPAST)            INNER JOIN DocFoldersByDocFolderID AS ddf1                  ON df1.PTSDocumentFolderID = ddf1.PTSDocumentFolderID_Parent)-- Flatten out folder path, DocFolderSingleByDocFolderID(PTSDocumentFolderID_Original, sDocumentFolder)AS (SELECT dfbdf.PTSDocumentFolderID_Original            , 'sDocumentFolder' = STUFF((SELECT '\' + sDocumentFolder                                         FROM DocFoldersByDocFolderID                                         WHERE (PTSDocumentFolderID_Original = dfbdf.PTSDocumentFolderID_Original)                                         ORDER BY PTSDocumentFolderID_Original, nLevel                                         FOR XML PATH ('')),1,1,'')      FROM DocFoldersByDocFolderID AS dfbdf      GROUP BY dfbdf.PTSDocumentFolderID_Original) And voila, I use the second CTE to join back to my original query (which is now a CTE for Source as we can now use MERGE to do INSERT and UPDATE at the same time).Each part of this solution would not solve the problem by itself because:If I don't use recursion, I cannot build out the path properly.  If I use the XML trick only, then I don't have the originating folder ID info that I need to link to the document.If I don't use the XML trick, then I don't have one row per document to show in the report.I could conceivably do this in the report function, but I'd rather not deal with the beginning or ending backslash and how to attach the document name.PIVOT doesn't do strings and UNPIVOT runs into the same problem as the above.I'm excited that each version of SQL server provides us new tools to solve old problems and/or enables us to solve problems in a more elegant wayThe 2 posts that helped me along:Recursive Queries Using Common Table ExpressionHow to use GROUP BY to concatenate strings in SQL server?

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• How to factor out data layer in nopCommerce and replace MS SQL with RavenDB?

  - by Kaveh Shahbazian

  I am new to nopCommerce and ecommerce in general but I am involved in an ecommerce project. Now from my past experiences with RavenDB (which mostly were absolutely pleasant) and based on the needs of the business (fast changes with awkward business workflows) It seemed to be an appealing option to have RavenDB handling all sort of things related to the database. I do not understand design and architecture of nopCommerce fully so I did not reach to a conclusion on how to factor data parts, since it seems the services layer actually does not abstract data-layer concepts away; like bringing in EF working model to other layers. I have found another project which used NuDB as it's database as a nopCommerce fork. But it did not help because NuDB still has the feeling of a RDBMS and is not as different as RavenDB. Now first how can I learn about the internals of nopCommerce (other than investigating the code)? It's workflows? It's conventions? Second has anyone tried something similar before with a NoSQL database (say like MongoDB or RavenDB)? Is it possible to achieve this in a 1 (~2) month time frame? Thanks in advance;

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• Mysql Sub Select Query Optimization

  - by Matt

  I'm running a query daily to compile stats - but it seems really inefficient. This is the Query: SELECT a.id, tstamp, label_id, (SELECT author_id FROM b WHERE b.tid = a.id ORDER BY b.tstamp DESC LIMIT 1) AS author_id FROM a, b WHERE (status = '2' OR status = '3') AND category != 6 AND a.id = b.tid AND (b.type = 'C' OR b.type = 'R') AND a.tstamp1 BETWEEN {$timestamp_start} AND {$timestamp_end} ORDER BY b.tstamp DESC LIMIT 500 This query seems to run really slow. Apologies for the crap naming - I've been asked to not reveal the actual table names. The reason there is a sub select is because the outer select gets one row from the table a and it gets a row from table b. But also need to know the latest author_id from table b as well, so I run a subselect to return that one. I don't want to run another select inside a php loop - as that is also inefficient. It works correctly - I just need to find a much faster way of getting this data set.

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• Linq query challenge

  - by vdh_ant

  My table structure is as follows: Person 1-M PesonAddress Person 1-M PesonPhone Person 1-M PesonEmail Person 1-M Contract Contract M-M Program Contract M-1 Organization At the end of this query I need a populated object graph where each person has their: PesonAddress's PesonPhone's PesonEmail's PesonPhone's Contract's - and this has its respective Program's Now I had the following query and I thought that it was working great, but it has a couple of problems: from people in ctx.People.Include("PersonAddress") .Include("PersonLandline") .Include("PersonMobile") .Include("PersonEmail") .Include("Contract") .Include("Contract.Program") where people.Contract.Any( contract => (param.OrganizationId == contract.OrganizationId) && contract.Program.Any( contractProgram => (param.ProgramId == contractProgram.ProgramId))) select people; The problem is that it filters the person to the criteria but not the Contracts or the Contract's Programs. It brings back all Contracts that each person has not just the ones that have an OrganizationId of x and the same goes for each of those Contract's Programs respectively. What I want is only the people that have at least one contract with an OrgId of x with and where that contract has a Program with the Id of y... and for the object graph that is returned to have only the contracts that match and programs within that contract that match. I kinda understand why its not working, but I don't know how to change it so it is working... This is my attempt thus far: from people in ctx.People.Include("PersonAddress") .Include("PersonLandline") .Include("PersonMobile") .Include("PersonEmail") .Include("Contract") .Include("Contract.Program") let currentContracts = from contract in people.Contract where (param.OrganizationId == contract.OrganizationId) select contract let currentContractPrograms = from contractProgram in currentContracts let temp = from x in contractProgram.Program where (param.ProgramId == contractProgram.ProgramId) select x where temp.Any() select temp where currentContracts.Any() && currentContractPrograms.Any() select new Person { PersonId = people.PersonId, FirstName = people.FirstName, ..., ...., MiddleName = people.MiddleName, Surname = people.Surname, ..., ...., Gender = people.Gender, DateOfBirth = people.DateOfBirth, ..., ...., Contract = currentContracts, ... }; //This doesn't work But this has several problems (where the Person type is an EF object): I am left to do the mapping by myself, which in this case there is quite a lot to map When ever I try to map a list to a property (i.e. Scholarship = currentScholarships) it says I can't because IEnumerable is trying to be cast to EntityCollection Include doesn't work Hence how do I get this to work. Keeping in mind that I am trying to do this as a compiled query so I think that means anonymous types are out.

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• Linq guru - filtering related entities...

  - by vdh_ant

  My table structure is as follows: Person 1-M PesonAddress Person 1-M PesonPhone Person 1-M PesonEmail Person 1-M Contract Contract M-M Program Contract M-1 Organization At the end of this query I need a populated object graph where each person has their: PesonAddress's PesonPhone's PesonEmail's PesonPhone's Contract's - and this has its respective Program's Now I had the following query and I thought that it was working great, but it has a couple of problems: from people in ctx.People.Include("PersonAddress") .Include("PersonLandline") .Include("PersonMobile") .Include("PersonEmail") .Include("Contract") .Include("Contract.Program") where people.Contract.Any( contract => (param.OrganizationId == contract.OrganizationId) && contract.Program.Any( contractProgram => (param.ProgramId == contractProgram.ProgramId))) select people; The problem is that it filters the person to the criteria but not the Contracts or the Contract's Programs. It brings back all Contracts that each person has not just the ones that have an OrganizationId of x and the same goes for each of those Contract's Programs respectively. What I want is only the people that have at least one contract with an OrgId of x with and where that contract has a Program with the Id of y... and for the object graph that is returned to have only the contracts that match and programs within that contract that match. I kinda understand why its not working, but I don't know how to change it so it is working... This is my attempt thus far: from people in ctx.People.Include("PersonAddress") .Include("PersonLandline") .Include("PersonMobile") .Include("PersonEmail") .Include("Contract") .Include("Contract.Program") let currentContracts = from contract in people.Contract where (param.OrganizationId == contract.OrganizationId) select contract let currentContractPrograms = from contractProgram in currentContracts let temp = from x in contractProgram.Program where (param.ProgramId == contractProgram.ProgramId) select x where temp.Any() select temp where currentContracts.Any() && currentContractPrograms.Any() select new Person { PersonId = people.PersonId, FirstName = people.FirstName, ..., ...., MiddleName = people.MiddleName, Surname = people.Surname, ..., ...., Gender = people.Gender, DateOfBirth = people.DateOfBirth, ..., ...., Contract = currentContracts, ... }; //This doesn't work But this has several problems (where the Person type is an EF object): I am left to do the mapping by myself, which in this case there is quite a lot to map When ever I try to map a list to a property (i.e. Scholarship = currentScholarships) it says I can't because IEnumerable is trying to be cast to EntityCollection Include doesn't work Hence how do I get this to work. Keeping in mind that I am trying to do this as a compiled query so I think that means anonymous types are out.

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• Python Permutation Program Flow help

  - by dsaccount1

  Hello world, i found this code at activestate, it takes a string and prints permutations of the string. I understand that its a recursive function but i dont really understand how it works, it'd be great if someone could walk me through the program flow, thanks a bunch! <pre><code> import sys def printList(alist, blist=[]): if not len(alist): print ''.join(blist) for i in range(len(alist)): blist.append(alist.pop(i)) printList(alist, blist) alist.insert(i, blist.pop()) if name == 'main': k='love' if len(sys.argv)1: k = sys.argv[1] printList(list(k))

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• Nested SELECT clause in SQL Compact 3.5

  - by Sasha

  In this post "select with nested select" I read that SQL Compact 3.5 (SP1) support nested SELECT clause. But my request not work: t1 - table 1 t2 - table 2 c1, c2 = columns select t1.c1, t1.c2, (select count(t2.c1) from t2 where t2.id = t1.id) as count_t from t1 Does SQL Compact 3.5 SP1 support nested SELECT clause in this case? Update: SQL Compact 3.5 SP1 work with this type of nested request: SELECT ... from ... where .. IN (SELECT ...) SELECT ... from (SELECT ...)

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• Alternative to sql NOT IN?

  - by Alex

  Hi, I am trying to make a materialized view in Oracle (I am a newbie, btw). For some reason, it doesn't like the presence of sub-query in it. I've been trying to use LEFT OUTER JOIN instead, but it's returning different data set now. Put simply, here's the code I'm trying to modify: SELECT * FROM table1 ros, table2 bal, table3 flx WHERE flx.name = 'XXX' AND flx.value = bal.value AND NVL (ros.ret, 'D') = Nvl (flx.attr16, 'D') AND ros.value = bal.segment3 AND ros.type IN ( 'AL', 'AS', 'PL' ) AND bal.period = 13 AND bal.code NOT IN (SELECT bal1.code FROM table2 bal1 WHERE bal1.value = flx.value AND bal1.segment3 = ros.value AND bal1.flag = bal.flag AND bal1.period = 12 AND bal1.year = bal.year) And here's one of my attempt: SELECT * FROM table1 ros, table2 bal, table3 flx LEFT OUTER JOIN table2 bal1 ON bal.code = bal1.code WHERE bal1.code is null AND bal1.segment3 = ros.value AND bal.segment3 = ros.value AND bal1.flag = bal.flag AND bal1.year = bal.year AND flx.name = 'XXX' AND flx.value = bal.value AND bal1.value = flx.value AND bal1.period_num = 12 AND NVL (ros.type, 'D') = NVL (flx.attr16, 'D') AND ros.value = bal.segment3 AND ros.type IN ( 'AL', 'AS', 'PL' ) AND bal.period = 13; This drives me nuts! Thanks in advance for the help :)

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• Fixing up an entity framework query

  - by vdh_ant

  My table structure is as follows: Person 1-M PesonAddress Person 1-M PesonPhone Person 1-M PesonEmail Person 1-M Contract Contract M-M Program Contract M-1 Organization At the end of this query I need a populated object graph where each person has their: PesonAddress's PesonPhone's PesonEmail's PesonPhone's Contract's - and this has its respective Program's Now I had the following query and I thought that it was working great, but it has a couple of problems: from people in ctx.People.Include("PersonAddress") .Include("PersonLandline") .Include("PersonMobile") .Include("PersonEmail") .Include("Contract") .Include("Contract.Program") where people.Contract.Any( contract => (param.OrganizationId == contract.OrganizationId) && contract.Program.Any( contractProgram => (param.ProgramId == contractProgram.ProgramId))) select people; The problem is that it filters the person to the criteria but not the Contracts or the Contract's Programs. It brings back all Contracts that each person has not just the ones that have an OrganizationId of x and the same goes for each of those Contract's Programs respectively. What I want is only the people that have at least one contract with an OrgId of x with and where that contract has a Program with the Id of y... and for the object graph that is returned to have only the contracts that match and programs within that contract that match. I kinda understand why its not working, but I don't know how to change it so it is working... This is my attempt thus far: from people in ctx.People.Include("PersonAddress") .Include("PersonLandline") .Include("PersonMobile") .Include("PersonEmail") .Include("Contract") .Include("Contract.Program") let currentContracts = from contract in people.Contract where (param.OrganizationId == contract.OrganizationId) select contract let currentContractPrograms = from contractProgram in currentContracts let temp = from x in contractProgram.Program where (param.ProgramId == contractProgram.ProgramId) select x where temp.Any() select temp where currentContracts.Any() && currentContractPrograms.Any() select new Person { PersonId = people.PersonId, FirstName = people.FirstName, ..., ...., MiddleName = people.MiddleName, Surname = people.Surname, ..., ...., Gender = people.Gender, DateOfBirth = people.DateOfBirth, ..., ...., Contract = currentContracts, ... }; //This doesn't work But this has several problems (where the Person type is an EF object): I am left to do the mapping by myself, which in this case there is quite a lot to map When ever I try to map a list to a property (i.e. Scholarship = currentScholarships) it says I can't because IEnumerable is trying to be cast to EntityCollection Include doesn't work Hence how do I get this to work. Keeping in mind that I am trying to do this as a compiled query so I think that means anonymous types are out.

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• Help with SQL query (list strings and count in same query)

  - by Mestika

  Hi everybody, I’m working on a small kind of log system to a webpage, and I’m having some difficulties with a query I want to do multiple things. I have tried to do some nested / subqueries but can’t seem to get it right. I’ve two tables: User = {userid: int, username} Registered = {userid: int, favoriteid: int} What I need is a query to list all the userid’s and the usernames of each user. In addition, I also need to count the total number of favoriteid’s the user is registered with. A user who is not registered for any favorite must also be listed, but with the favorite count shown as zero. I hope that I have explained my request probably but otherwise please write back so I can elaborate. By the way, the query I’ve tried with look like this: SELECT user.userid, user.username FROM user,registered WHERE user.userid = registered.userid(SELECT COUNT(favoriteid) FROM registered) However, it doesn’t do the trick, unfortunately Kind regards Mestika

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• Recursion with an Array; can't get the right value to return

  - by Matt

  Recursive Solution: Not working! Explanation: An integer, time, is passed into the function. It's then used to provide an end to the FOR statement (counter<time). The IF section (time == 0) provides a base case where the recursion should terminate, returning 0. The ELSE section is where the recursive call occurs: total is a private variable defined in the header file, elsewhere. It's initialized to 0 in a constructor, elsewhere. The function calls itself, recursively, adding productsAndSales[time-1][0] to total, again, and again, until the base call. Then the total is returned, and printed out later. Well, that's what I hoped for anyway. What I imagined would happen is that I would add up all the values in this one column of the array and the value would get returned, and printed out. Instead if returns 0. If I set the IF section to "return 1", I noticed that it returns powers of 2, for whatever value time is. EG: Time = 3, it returns 2*2 + 1. If time = 5, it returns 2*2*2*2 + 1. I don't understand why it's not returning the value I'm expecting. int CompanySales::calcTotals( int time ) { cout << setw( 4 ); if ( time == 0 ) { return 0; } else { return total += calcTotals( productsAndSales[ time-1 ][ 0 ]); } } Iterative Solution: Working! Explanation: An integer, time, is passed into the function. It's then used to provide an end to the FOR statement (counter<time). The FOR statement cycles through an array, adding all of the values in one column together. The value is then returned (and elsewhere in the program, printed out). Works perfectly. int CompanySales::calcTotals( int time ) { int total = 0; cout << setw( 4 ); for ( int counter = 0; counter < time; counter++ ) { total += productsAndSales[counter][0]; } return total0; }

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• How to write a function to output unconstant loop

  - by tunpishuang

  Here is the function description test($argv) $argv is an array, for example $argv=array($from1,$to1,$from2,$to2.....); array items must be even. $argv=array(1,2,4,5) : this will output values like below: 1_4 1_5 2_4 2_5 The number of array $argv's is not constant. Maybe 3 or 4 levels of loop will be outputed. I know this will used RECURSIVE , but i don't know exactly how to code.

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• Aggregate Functions on subsets of data based on current row values with SQL

  - by aasukisuki

  Hopefully that title makes sense... Let's say I have an employee table: ID | Name | Title | Salary ---------------------------- 1 | Bob | Manager | 15285 2 | Joe | Worker | 10250 3 | Al | Worker | 11050 4 | Paul | Manager | 16025 5 | John | Worker | 10450 What I'd like to do is write a query that will give me the above table, along with an averaged salary column, based on the employee title: ID | Name | Title | Salary | Pos Avg -------------------------------------- 1 | Bob | Manager | 15285 | 15655 2 | Joe | Worker | 10250 | 10583 3 | Al | Worker | 11050 | 10583 4 | Paul | Manager | 16025 | 15655 5 | John | Worker | 10450 | 10583 I've tried doing this with a sub-query along the lines of: Select *, (select Avg(e2.salary) from employee e2 where e2.title = e.title) from employee e But I've come to realize that the sub-query is executed first, and has no knowledge of the table alias'd e I'm sure I'm missing something REALLY obvious here, can anyone point me in the right diretion?

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• how to write a function to output unconstant loop with PHP

  - by tunpishuang

  here is the function description test($argv) $argv is an array , for example $argv=array($from1,$to1,$from2,$to2.....); array items must be even. $argv=array(1,2,4,5) : this will output values like below: 1_4 1_5 2_4 2_5 the number of arrray $argv's is not constant. maybe 3 or 4 levels of loop will be outputed. i know this will used RECURSIVE , but i don't know exatly how to code.

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• What's the most efficient query?

  - by Aaron Carlino

  I have a table named Projects that has the following relationships: has many Contributions has many Payments In my result set, I need the following aggregate values: Number of unique contributors (DonorID on the Contribution table) Total contributed (SUM of Amount on Contribution table) Total paid (SUM of PaymentAmount on Payment table) Because there are so many aggregate functions and multiple joins, it gets messy do use standard aggregate functions the the GROUP BY clause. I also need the ability to sort and filter these fields. So I've come up with two options: Using subqueries: SELECT Project.ID AS PROJECT_ID, (SELECT SUM(PaymentAmount) FROM Payment WHERE ProjectID = PROJECT_ID) AS TotalPaidBack, (SELECT COUNT(DISTINCT DonorID) FROM Contribution WHERE RecipientID = PROJECT_ID) AS ContributorCount, (SELECT SUM(Amount) FROM Contribution WHERE RecipientID = PROJECT_ID) AS TotalReceived FROM Project; Using a temporary table: DROP TABLE IF EXISTS Project_Temp; CREATE TEMPORARY TABLE Project_Temp (project_id INT NOT NULL, total_payments INT, total_donors INT, total_received INT, PRIMARY KEY(project_id)) ENGINE=MEMORY; INSERT INTO Project_Temp (project_id,total_payments) SELECT `Project`.ID, IFNULL(SUM(PaymentAmount),0) FROM `Project` LEFT JOIN `Payment` ON ProjectID = `Project`.ID GROUP BY 1; INSERT INTO Project_Temp (project_id,total_donors,total_received) SELECT `Project`.ID, IFNULL(COUNT(DISTINCT DonorID),0), IFNULL(SUM(Amount),0) FROM `Project` LEFT JOIN `Contribution` ON RecipientID = `Project`.ID GROUP BY 1 ON DUPLICATE KEY UPDATE total_donors = VALUES(total_donors), total_received = VALUES(total_received); SELECT * FROM Project_Temp; Tests for both are pretty comparable, in the 0.7 - 0.8 seconds range with 1,000 rows. But I'm really concerned about scalability, and I don't want to have to re-engineer everything as my tables grow. What's the best approach?

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• Speeding up inner-joins and subqueries while restricting row size and table membership

  - by hiffy

  I'm developing an rss feed reader that uses a bayesian filter to filter out boring blog posts. The Stream table is meant to act as a FIFO buffer from which the webapp will consume 'entries'. I use it to store the temporary relationship between entries, users and bayesian filter classifications. After a user marks an entry as read, it will be added to the metadata table (so that a user isn't presented with material they have already read), and deleted from the stream table. Every three minutes, a background process will repopulate the Stream table with new entries (i.e. whenever the daemon adds new entries after the checks the rss feeds for updates). Problem: The query I came up with is hella slow. More importantly, the Stream table only needs to hold one hundred unread entries at a time; it'll reduce duplication, make processing faster and give me some flexibility with how I display the entries. The query (takes about 9 seconds on 3600 items with no indexes): insert into stream(entry_id, user_id) select entries.id, subscriptions_users.user_id from entries inner join subscriptions_users on subscriptions_users.subscription_id = entries.subscription_id where subscriptions_users.user_id = 1 and entries.id not in (select entry_id from metadata where metadata.user_id = 1) and entries.id not in (select entry_id from stream where user_id = 1); The query explained: insert into stream all of the entries from a user's subscription list (subscriptions_users) that the user has not read (i.e. do not exist in metadata) and which do not already exist in the stream. Attempted solution: adding limit 100 to the end speeds up the query considerably, but upon repeated executions will keep on adding a different set of 100 entries that do not already exist in the table (with each successful query taking longer and longer). This is close but not quite what I wanted to do. Does anyone have any advice (nosql?) or know a more efficient way of composing the query?

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• Using subselect to accomplish LEFT JOIN

  - by Andre

  Is is possible to accomplish the equivalent of a LEFT JOIN with subselect where multiple columns are required. Here's what I mean. SELECT m.*, (SELECT * FROM model WHERE id = m.id LIMIT 1) AS models FROM make m As it stands now doing this gives me a 'Operand should contain 1 column(s)' error. Yes I know this is possible with LEFT JOIN, but I was told it was possible with subselect to I'm curious as to how it's done.

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• Joins and subqueries in LINQ

  - by Brian

  I am trying to do a join with a sub query and can't seem to get it. Here is what is looks like working in sql. How do I get to to work in linq? SELECT po.*, p.PermissionID FROM PermissibleObjects po INNER JOIN PermissibleObjects_Permissions po_p ON (po.PermissibleObjectID = po_p.PermissibleObjectID) INNER JOIN Permissions p ON (po_p.PermissionID = p.PermissionID) LEFT OUTER JOIN ( SELECT u_po.PermissionID, u_po.PermissibleObjectID FROM Users_PermissibleObjects u_po WHERE u_po.UserID = '2F160457-7355-4B59-861F-9871A45FD166' ) used ON (p.PermissionID = used.PermissionID AND po.PermissibleObjectID = used.PermissibleObjectID) WHERE used.PermissionID is null

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• MySQL Sub-query.. Doesn't provide proper information after 3 entries into table.

  - by Chris Keefer

  After I get 3 rows in my forum_threads table this no longer does it's job; to organize a list of active forum threads and put the most recently responded-to thread at the top of the list, followed by second most recent posted-to thread, followed by third, fourth, etc. Like I said, the query works wonders up until there is a fourth row added to forum_threads. SELECT forum_threads.*, forum_posts.thread_id FROM forum_threads INNER JOIN (SELECT MAX(id) AS id, thread_id as thread_id FROM forum_posts group by thread_id order by id DESC) forum_posts ON forum_threads.id = forum_posts.thread_id

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• Showing all rows for keys with more than one row

  - by Leif Neland

  Table kal id integer primary key init char 4 indexed job char4 id init job --+----+------ 1 | aa | job1 2 | aa | job2 3 | bb | job1 4 | cc | job3 5 | cc | job5 I want to show all rows where init has more than one row id init job --+----+------ 1 | aa | job1 2 | aa | job2 4 | cc | job3 5 | cc | job5 I tried select * from kal where init in (select init from kal group by init having count(init)2); Actually, the table has 60000 rows, and the query was count(init)<40, but it takes humongus time, phpmyadmin and my patience runs out. Both select init from kal group by init having count(init)2) and select * from kal where init in ('aa','bb','cc') runs in "no time", less than 0.02 seconds. I've tried different subqueries, but all takes "infinite" time, more than a few minutes; I've actually never let them finish. Leif

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• Linq query challenge - can this be done?

  - by vdh_ant

  My table structure is as follows: Person 1-M PesonAddress Person 1-M PesonPhone Person 1-M PesonEmail Person 1-M Contract Contract M-M Program Contract M-1 Organization At the end of this query I need a populated object graph where each person has their: PesonAddress's PesonPhone's PesonEmail's PesonPhone's Contract's - and this has its respective Program's Now I had the following query and I thought that it was working great, but it has a couple of problems: from people in ctx.People.Include("PersonAddress") .Include("PersonLandline") .Include("PersonMobile") .Include("PersonEmail") .Include("Contract") .Include("Contract.Program") where people.Contract.Any( contract => (param.OrganizationId == contract.OrganizationId) && contract.Program.Any( contractProgram => (param.ProgramId == contractProgram.ProgramId))) select people; The problem is that it filters the person to the criteria but not the Contracts or the Contract's Programs. It brings back all Contracts that each person has not just the ones that have an OrganizationId of x and the same goes for each of those Contract's Programs respectively. What I want is only the people that have at least one contract with an OrgId of x with and where that contract has a Program with the Id of y... and for the object graph that is returned to have only the contracts that match and programs within that contract that match. I kinda understand why its not working, but I don't know how to change it so it is working... This is my attempt thus far: from people in ctx.People.Include("PersonAddress") .Include("PersonLandline") .Include("PersonMobile") .Include("PersonEmail") .Include("Contract") .Include("Contract.Program") let currentContracts = from contract in people.Contract where (param.OrganizationId == contract.OrganizationId) select contract let currentContractPrograms = from contractProgram in currentContracts let temp = from x in contractProgram.Program where (param.ProgramId == contractProgram.ProgramId) select x where temp.Any() select temp where currentContracts.Any() && currentContractPrograms.Any() select new Person { PersonId = people.PersonId, FirstName = people.FirstName, ..., ...., MiddleName = people.MiddleName, Surname = people.Surname, ..., ...., Gender = people.Gender, DateOfBirth = people.DateOfBirth, ..., ...., Contract = currentContracts, ... }; //This doesn't work But this has several problems (where the Person type is an EF object): I am left to do the mapping by myself, which in this case there is quite a lot to map When ever I try to map a list to a property (i.e. Scholarship = currentScholarships) it says I can't because IEnumerable is trying to be cast to EntityCollection Include doesn't work Hence how do I get this to work. Keeping in mind that I am trying to do this as a compiled query so I think that means anonymous types are out.

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