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• Does having a longer string in a SQL Like expression allow hinder or help query executing speed?

  - by Allain Lalonde

  I have a db query that'll cause a full table scan using a like clause and came upon a question I was curious about... Which of the following should run faster in Mysql or would they both run at the same speed? Benchmarking might answer it in my case, but I'd like to know the why of the answer. The column being filtered contains a couple thousand characters if that's important. SELECT * FROM users WHERE data LIKE '%=12345%' or SELECT * FROM users WHERE data LIKE '%proileId=12345%' I can come up for reasons why each of these might out perform the other, but I'm curious to know the logic.

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• [C#] How to create a constructor of a class that return a collection of instances of that class?

  - by codemonkie

  My program has the following class definition: public sealed class Subscriber { private subscription; public Subscriber(int id) { using (DataContext dc = new DataContext()) { this.subscription = dc._GetSubscription(id).SingleOrDefault(); } } } ,where _GetSubscription() is a sproc which returns a value of type ISingleResult<_GetSubscriptionResult> Say, I have a list of type List<int> full of 1000 ids and I want to create a collection of subscribers of type List<Subscriber>. How can I do that without calling the constructor in a loop for 1000 times? Since I am trying to avoid switching the DataContext on/off so frequently that may stress the database. TIA.

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• Are indexes good or bad for a large database?

  - by gmemon

  Hello All, I read on MySQL Performance Blog that when tables are large, it is better to scan full tables, instead of using indexes. I have a table with tens of millions of rows. When conducting queries, if I use no indexes, then queries are 24 times slower than with indexes. I know lot of things may cause this (e.g., are rows stored sequentially), but can you please give me some hints what might be happening? Or how I should start examining this issue? I want to understand when use of indexes is preferred and when it's not Thanks

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• Can't delete record via the datacontext it was retrieved from

  - by Antilogic

  I just upgraded one of my application's methods to use compiled queries (not sure if this is relevant). Now I'm getting contradicting error messages when I run the code. This is my method: MyClass existing = Queries.MyStaticCompiledQuery(MyRequestScopedDataContext, param1, param2).SingleOrDefault(); if (existing != null) { MyRequestScopedDataContext.MyClasses.DeleteOnSubmit(existing); } When I run it I get this message: Cannot remove an entity that has not been attached. Note that the compiled query and the DeleteOnSubmit reference the same DataContext. Still I figured I'd humor the application and add an attach command before the DeleteOnSubmit, like so: MyClass existing = Queries.MyStaticCompiledQuery(MyRequestScopedDataContext, param1, param2).SingleOrDefault(); if (existing != null) { MyRequestScopedDataContext.MyClasses.Attach(existing); MyRequestScopedDataContext.MyClasses.DeleteOnSubmit(existing); } BUT... When I run this code, I get a completely different contradictory error message: An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. This is not supported. I'm at a complete loss... Does anyone else have some insight as to why I can't delete a record via the same DataContext I retrieved it from?

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• How to analyse Wikipedia article's data base with R?

  - by Tal Galili

  Hi all, This is a "big" question, that I don't know how to start, so I hope some of you can give me a direction. And if this is not a "good" question, I will close the thread with an apology. I wish to go through the database of Wikipedia (let's say the English one), and do statistics. For example, I am interested in how many active editors (which should be defined) Wikipedia had at each point of time (let's say in the last 2 years). I don't know how to build such a database, how to access it, how to know which types of data it has and so on. So my questions are: What tools do I need for this (besides basic R) ? MySQL on my computer? RODBC database connection? How do you start planning for such a project?

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• Bit convector : Get byte array from string

  - by nCdy

  When I have a string like "0xd8 0xff 0xe0" I do Text.Split(' ').Select(part => byte.Parse(part, System.Globalization.NumberStyles.HexNumber)).ToArray(); But if I got string like "0xd8ffe0" I don't know what to do ? also I'm able for recommendations how to write byte array as one string.

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• VB.NET logical expression evaluator

  - by Tim

  I need to test a logical expression held in a string to see if it evaluate to TRUE or FALSE.(the strig is built dynamically) For example the resulting string may contain "'dog'<'cat' OR (14 AND 4<6)". There are no variables in the string, it will logically evaluate. It will only contain simple operators = < < = <= and AND , OR and Open and Close Brackets, string constants and numbers. (converted to correct syntax && || etc.) I currently acheive this by creating a jscipt function and compiling it into a .dll. I then reference the .dll in my VB.NET project. class ExpressionEvaluator { function Evaluate(Expression : String) { return eval(Expression); } } Is there a simpler method using built in .NET functions or Lamdba expressions.

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• How to fetch a random record from SQLite database?

  - by Bruce

  I am working on PHP. I was working with MySQL before. Here is the code I used - $offset_result = mysqli_query($con, " SELECT FLOOR(RAND() * COUNT(*)) AS `offset` FROM students "); $offset_row = mysqli_fetch_object( $offset_result ); $offset = $offset_row->offset; $result = mysqli_query($con, " SELECT name FROM students LIMIT $offset, 1 " ); $row = mysqli_fetch_row($result); mysqli_free_result($result); What will be the corresponding set of statements for SQLite?

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• How is this website fixing the encoding ??

  - by Tal Galili

  Hi all, I am trying to turn this text: ×וויר. העתיד של רשתות חברתיות והתקשורת ×©×œ× ×• Into this text: ?????. ????? ?? ????? ??????? ???????? ???? Somehow, this website: http://www.pixiesoft.com/flip/ Can do it, and I would like to know how I might be able to do it myself (with whatever programming language or software) Just saving the file as UTF8 won't do it. My motivation for this question is that I have a friend's exported XML file with the garbled text which I want to turn into corrected Hebrew text file. The XML export was originally garbled by MySQL import and exports, but I don't have the information needed to fix it or traceback the problem. Thanks.

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• Cannot perform an ORDERBY against my EF4 data

  - by Jaxidian

  I have a query hitting EF4 using STEs and I'm having an issue with user-defined sorting. In debugging this, I have removed the dynamic sorting and am hard-coding it and I still have the issue. If I swap/uncomment the var results = xxx lines in GetMyBusinesses(), my results are not sorted any differently - they are always sorting it ascendingly. FYI, Name is a varchar(200) field in SQL 2008 on my Business table. private IQueryable<Business> GetMyBusinesses(MyDBContext CurrentContext) { var myBusinesses = from a in CurrentContext.A join f in CurrentContext.F on a.FID equals f.id join b in CurrentContext.Businesses on f.BID equals b.id where a.PersonID == 52 select b; var results = from r in myBusinesses orderby "Name" ascending select r; //var results = from r in results // orderby "Name" descending // select r; return results; } private PartialEntitiesList<Business> DoStuff() { var myBusinesses = GetMyBusinesses(); var myBusinessesCount = GetMyBusinesses().Count(); Results = new PartialEntitiesList<Business>(myBusinesses.Skip((PageNumber - 1)*PageSize).Take(PageSize).ToList()) {UnpartialTotalCount = myBusinessesCount}; return Results; } public class PartialEntitiesList<T> : List<T> { public PartialEntitiesList() { } public PartialEntitiesList(int capacity) : base(capacity) { } public PartialEntitiesList(IEnumerable<T> collection) : base(collection) { } public int UnpartialTotalCount { get; set; } }

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• PDO Prepare statement not processing parameters

  - by Danten

  I've exhausted all efforts at what appears to be a trivial problem, but gotten nowhere. There is a simple Prepare statement: $qry = $core->db->prepare("SELECT * FROM users WHERE email = '?'"); $qry->execute(array('[email protected]')); However, no rows are returned. Running the query with the parameters hardcoded into the query results in a successful selection of one row. I've tryed many different methods of doing the prepare, but even it this most simple form it isn't working. The PDO object is stored in a singleton called Core. PDO is using the mysql driver.

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• How to Select two values from one value

  - by Jacob Seleznev

  I want to do something like this: foreach (Customer c in customers) { yield return c.Name; yield return "0"; } I started: customers.Select(c => new { c.Name, Second = "0" }).??? But then what?

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• Is it possible to load an entire SQL Server CE database into RAM?

  - by DanM

  I'm using LinqToSql to query a small SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table via a foreign key, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of the appeal of LinqToSql. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view.

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• Removing certain characters in all rows that match a regex?

  - by user001

  I'd like to change {foo, {bar}, foobar} to {foo, bar, foobar} in all rows that match '{.*{'. I.e. remove all curly braces { and } except the outer most pair. So doing mysql -h $H -u $U -p$P $DB -B -e "SELECT id FROM t WHERE col REGEXP '{.*{'" > bad.txt selects all the rows that will need this substitution. How do I make this substitution very quickly? EDIT: Could I do it by update table set column = REPLACE(column,'{',''); Then restore the out most pair update table set column = REPLACE(column,'^','{'); update table set column = REPLACE(column,'$','}');

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• Change update value of property (LINQTOSQL)

  - by Dynde

  Hi... I've got an entity object - Customer, with a property called VATRate. This VATRate is in the form of a decimal (0.25). I wanted to be able to enter a percentage value, and save it in the correct decimal value in the database, so I made this custom property: partial class Customer{ public decimal VatPercent { get{ ... //Get code works fine} set { this.VATRate = (value / 100); } } } And then I just bind this property instead of VATRate in my ASPX editTemplate (formview). This actually works - at least one time, when I debug an update, the value is set correctly one time, and then right after it gets set to the old value. I can't really see why it sets the value twice (and with the old value the second time). Can anyone shed some light on this?

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• Problem storing string containing quotes

  - by Jack

  I have the following table - $sql = "CREATE TABLE received_queries ( sender_screen_name varchar(50), text varchar(150) )"; I use the following SQL statement to store values in the table $sql = "INSERT INTO received_queries VALUES ('$sender_screen_name', '$text')"; Now I am trying to store the following string as 'text'. One more #haiku: Cotton wool in mind; feeling like a sleep won't cure; I need some coffee. and I get the following error message Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 't cure; I need some coffee.')' at line 1 I think must be a pretty common problem. How do I solve it?

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• How can I bind an Enum to a DbType of bit or int?

  - by uriDium

  Hi I am using Linq2Sql and want to bind an objects field (which is enum) to either a bit or a int type in the database. For example I want have a gender field in my model. I have already edited the DBML and changed the Type to point to my enum. I want to create Radio buttons (which I think I have figured out) for gender and dropdown lists for other areas using the same idea. My enum looks like this public enum Gender { Male, Female } Mapping between DbType 'int' and Type 'Project.Models.Gender' in Column 'Gender' of Type 'Candidate' is not supported. Any ideas on how to do this mapping. Am I missing something on the enums.

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• usage of intval & real_escape_string when sanitizing integers

  - by paulus

  dear All. I'm using integer PKs in some tables of mysql database. Before input from PHP script, I am doing some sanitizing, which includes intval($id) and $mysqli-real_escape_string(). The queries are quite simple insert into `tblproducts`(`supplier_id`,`description`) values('$supplier_id','$description') In this example, $description goes through real_escape_string(), while $supplier_id only being intval()'ed. I'm just curious, if there're any situations, when I need to apply both intval and real_escape_string to integer I'm inserting into DB? So basically do I really need to use? $supplier_id = intval($mysqli->real_escape_string($supplier_id)); Thank you.

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• Is there any significant difference between List.Last() and List.Last<T>()?

  - by edg

  Given a list of rectangles, var myList = new List<Rectangle>(); I cannot add anything but Rectangles to this list, so what factors would make me prefer Rectangle lastRect = myList.Last<Rectangle>(); over simply Rectangle lastRect = myList.Last();

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• count of last item of the day

  - by frenchie

  I have a query in which one of the fields contains the count of status. The status can change several times a day and the count should be based on the final status of the day. For instance, this is what I have for Status1. CountStatus1 = (from status in MyDataContext.StatusHistories where status.UserID == TheUserID where status.StatusDateTime.Month == TheMonth.Month where status.StatusDateTime.Year == TheMonth.Year where status.NewStatus == 1 // where the LAST STATUS OF THE DAY == 1 select status.StatusID).Count() The problem is that I want to select the last status of the day to be equal to 1, and count those. The status for a day can change from 1 to 4 to 2 to 5 to 3 and then to finally to 1; if I write the query like this, the count will include 2 1's and then the 4,2,5 and 3 will also be counted in CountStatus4, CountStatus3, CountStatus"n". The return data is a monthly report grouped by day, where each day is a row. The structure of the query looks like this: var OutputStatusReport = from w in MyDataContext.WorkHistory where w.UserID == TheUserID where w.WorkDatetime.Month == TheMonth.Month where w.WorkDatetime.Year == TheMonth.Year group w by w.Datetime.Date into daygroups select new MyObjectModel { CountStatus1 = ...., CountStatus2 = ...., CountStatus3 =...... }; So I need the day of the count to match the day of daygroups. I'm struggling to figure this one out and any help is very welcome. Thanks.

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• Is Entity Framework more mockable than Linq2Sql?

  - by lance

  I've found that Linq2Sql doesn't (Rhino) mock well, as the interfaces I need aren't there. Does EF generate code that's more mockable? NOTE: I'm not mocking, yet, without interfaces, the next reader of this question may not have my bias. EDIT: VS2008 / 3.5 for now.

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• ASP.net MVC3 howto edit sql database

  - by user1662380

  MovieStoreEntities MovieDb = new MovieStoreEntities(); public ActionResult Edit(int id) { //var EditMovie1 = MovieDb AddMovieModel EditMovie = (from M in MovieDb.Movies from C in MovieDb.Categories where M.CategoryId == C.Id where M.Id == id select new AddMovieModel { Name = M.Name, Director = M.Director, Country = M.Country, categorie = C.CategoryName, Category = M.CategoryId }).FirstOrDefault(); //AddMovieModel EditMovie1 = MovieDb.Movies.Where(m => m.Id == id).Select(m => new AddMovieModel {m.Id }).First(); List<CategoryModel> categories = MovieDb.Categories .Select(category => new CategoryModel { Category = category.CategoryName, id = category.Id }) .ToList(); ViewBag.Category = new SelectList(categories, "Id", "Category"); return View(EditMovie); } // // POST: /Default1/Edit/5 [HttpPost] public ActionResult Edit(AddMovieModel Model2) { List<CategoryModel> categories = MovieDb.Categories .Select(category => new CategoryModel { Category = category.CategoryName, id = category.Id }) .ToList(); ViewBag.Category = new SelectList(categories, "Id", "Category"); if (ModelState.IsValid) { //MovieStoreEntities model = new MovieStoreEntities(); MovieDb.SaveChanges(); return View("Thanks2", Model2); } else return View(); } This is the Code that I have wrote to edit Movie details and update database in the sql server. This dont have any compile errors, But It didnt update sql server database.

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• PHP PDO Username Availability Checker

  - by John Bernal

  I'm building a registration page that uses JQuery's validator plugin to validate the form. For the username, i used the remote method. So here's my jquery+html code: fiddle And here's Available.php: <?php $usr = $_POST["username"]; $link = new PDO('mysql:***;dbname=***;charset=UTF-8','***','***'); $usr_check = $link->prepare("SELECT * FROM Conference WHERE Username = :usr"); $link->bindParam(':usr', $usr); $usr_check->execute(); if($usr_check->rowCount()>0) echo "false"; else echo "true"; ?> So I have a test account in my database with the username: user. When I tried to submit my form with the same username, it didn't display the error saying "username taken" which means the php isn't correct. Any ideas where I went wrong? Thanks

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• Sync database from desktop system to remote server and vice versa?

  - by qulzam

  I make a application, which has to interfaces. one is desktop and other is web application. both have their own databases (which are same is structure). I want to sync the database from desktop to remote server and also from remote server to desktop but i have no idea that how it does. I use the MYSql database. and my desktop application is in .NET NOTE: There are more than one destop systems who update their databases and also sync databases.

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• Refreshing <div> and load data from php

  - by forgatn

  I have on my page and there is a tag where is some and values filled from mySQL DB. I need some JavaScript I think. When I select one option, I want to display in this propriate DATAs which are in DB. without refreshing whole page. Can you tell me how to do it, if you know that please?:) <div id="country1" class="tabcontent"> <label>Choose protocol</label> <SELECT name="cisloprot"> <?php $con = mysql_connect("localhost", "root", "123456"); $sql = "SELECT kod FROM prot GROUP BY kod"; $rs = mysql_query($sql,$con); while ($r = mysql_fetch_array($rs)) { echo "<OPTION VALUE=".$r['kod'].">".$r['kod']."</OPTION>"; } ?> </SELECT> </div>

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