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  • How can I synchronize database access between a write-thread and a read-thread?

    - by Runcible
    My program has two threads: Main execution thread that handles user input and queues up database writes A utility thread that wakes up every second and flushes the writes to the database Inside the main thread, I occasionally need to make reads on the database. When this happens, performance is not important, but correctness is. (In a perfect world, I would be reading from a cache, not making a round-trip to the database - but let's put that aside for the sake of discussion.) How do I make sure that the main thread sees a correct / quiescent database? A standard mutex won't work, since I run the risk of having the main thread grab the mutex before the data gets flushed to the database. This would be a big race condition. What I really want is some sort of mutex that lets the main thread of execution proceed only AFTER the mutex has been grabbed and released once. Does such a thing exist? What's the best way to solve this problem?

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  • What are some methods to prevent double posting in a form? (PHP)

    - by jpjp
    I want to prevent users from accidentally posting a comment twice. I use the PRG (post redirect get) method, so that I insert the data on another page then redirect the user back to the page which shows the comment. This allows users to refresh as many times as they want. However this doesn't work when the user goes back and clicks submit again or when they click submit 100 times really fast. I don't want 100 of the same comments. I looked at related questions on SO and found that a token is best. But I am having trouble using it. //makerandomtoken(20) returns a random 20 length char. <form method="post" ... > <input type="text" id="comments" name="comments" class="commentbox" /><br/> <input type="hidden" name="_token" value="<?php echo $token=makerandomtoken(20); ?>" /> <input type="submit" value="submit" name="submit" /> </form> if (isset($_POST['submit']) && !empty($comments)) { $comments= mysqli_real_escape_string($dbc,trim($_POST['comments'])); //how do I make the if-statment to check if the token has been already set once? if ( ____________){ //don't insert comment because already clicked submit } else{ //insert the comment into the database } } So I have the token as a hidden value, but how do I use that to prevent multiple clicking of submit. METHODS: someone suggested using sessions. I would set the random token to $_SESSION['_token'] and check if that session token is equal to the $_POST['_token'], but how do I do that? When I tried, it still doesn't check

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  • Nested query to find details in table B for maximum value in table A

    - by jpatokal
    I've got a huge bunch of flights travelling between airports. Each airport has an ID and (x,y) coordinates. For a given list of flights, I want to find the northernmost (highest x) airport visited. Here's the query I'm currently using: SELECT name,iata,icao,apid,x,y FROM airports WHERE y=(SELECT MAX(y) FROM airports AS a , flights AS f WHERE (f.src_apid=a.apid OR f.dst_apid=a.apid) ) This works beautifully and reasonably fast as long as y is unique, but fails once it isn't. What I'd want to do instead is find the MAX(y) in the subquery, but return the unique apid for the airport with the highest y. Any suggestions?

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  • How to make an id auto_increment from where it last left off after a record delete?

    - by Sammy
    This isn't that big of a deal but I was wondering if it can be done. Right now when I insert a new record, the id field which is auto_increment and set as primary key increases it's value by one: id | first_name | last_name ------------------------------ 1 | John | Smith 2 | Jane | Doe But if I delete record 2, the next one I insert is going to have an id of 3. Is there any way to make it have an id of 2 automatically (without having to manually insert it)?

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  • Accessing data entered into multiple Django forms and generating them onto a new URL

    - by pedjk
    I have a projects page where users can start up new projects. Each project has two forms. The two forms are: class ProjectForm(forms.Form): Title = forms.CharField(max_length=100, widget=_hfill) class SsdForm(forms.Form): Status = forms.ModelChoiceField(queryset=P.ProjectStatus.objects.all()) With their respective models as follows: class Project(DeleteFlagModel): Title = models.CharField(max_length=100) class Ssd(models.Model): Status = models.ForeignKey(ProjectStatus) Now when a user fills out these two forms, the data is saved into the database. What I want to do is access this data and generate it onto a new URL. So I want to get the "Title" and the "Status" from these two forms and then show them on a new page for that one project. I don't want the "Title" and "Status" from all the projects to show up, just for one project at a time. If this makes sense, how would I do this? I'm very new to Django and Python (though I've read the Django tutorials) so I need as much help as possible. Thanks in advance Edit: The ProjectStatus code is (under models): class ProjectStatus(models.Model): Name = models.CharField(max_length=30) def __unicode__(self): return self.Name

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  • SQL Join query help

    - by lostInTransit
    Hi I have 2 tables A and B with the following columns Table A - id,bId,aName,aVal Table B - id,bName where A.bId is the same as B.id. I want a result set from a query to get A.id, A.aName, B.bName where A.bId=B.id OR A.id, A.aName, "" when A.bId=0. In both cases, only those records should be considered where A.aVal LIKE "aVal" Can someone please help me with the query? I can use left join but how do I get the blank string if bId=0 and B.bName otherwise? Thanks

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  • Very simple shopping cart, remove button

    - by Kynian
    Im writing sales software that will be walking through a set of pages and on certain pages there are items listed to sell and when you click buy it basically just passes a hidden variable to the next page to be set as a session variable, and then when you get to the end it call gets reported to a database. However my employer wanted me to include a shopping cart, and this shopping cart should display the item name, sku, and price of whatever you're buying, as well as a remove button so the person doing the script doesnt need to go back through the entire thing to remove one item. At the moment I have the cart set to display everything, which was fairly simple. but I cant figure out how to get the remove button to work. Here is the code for the shopping cart: $total = 0; //TEST CODE: $_SESSION['itemname-addon'] = "Test addon"; $_SESSION ['price-addon'] = 10.00; $_SESSION ['sku-addon'] = "1234h"; $_SESSION['itemname-addon1'] = "Test addon1"; $_SESSION ['price-addon1'] = 99.90; $_SESSION ['sku-addon1'] = "1111"; $_SESSION['itemname-addon2'] = "Test addon2"; $_SESSION ['price-addon2'] = 19.10; $_SESSION ['sku-addon2'] = "123"; //end test code $items = Array ( "0"=> Array ( "name" => $_SESSION['itemname-mo'], "price" => $_SESSION ['price-mo'], "sku" => $_SESSION ['sku-mo'] ), "1" => Array ( "name" => $_SESSION['itemname-addon'], "price" => $_SESSION ['price-addon'], "sku" => $_SESSION ['sku-addon'] ), "2" => Array ( "name" => $_SESSION['itemname-addon1'], "price" => $_SESSION ['price-addon1'], "sku" => $_SESSION ['sku-addon1'] ), "3" => Array ( "name" => $_SESSION['itemname-addon2'], "price" => $_SESSION ['price-addon2'], "sku" => $_SESSION ['sku-addon2'] ) ); $a_length = count($items); for($x = 0; $x<$a_length; $x++){ $total +=$items[$x]['price']; } $formattedtotal = number_format($total,2,'.',''); for($i = 0; $i < $a_length; $i++){ $name = $items[$i]['name']; $price = $items[$i]['price']; $sku = $items[$i]['sku']; displaycart($name,$price,$sku); } echo "<br /> <b>Sub Total:</b> $$formattedtotal"; function displaycart($name,$price,$sku){ if($name != null || $price != null || $sku != null){ if ($name == "no sale" || $price == "no sale" || $sku == "no sale"){ echo ""; } else{ $formattedprice = number_format($price,2,'.',''); echo "$name: $$formattedprice ($sku)"; echo "<form action=\"\" method=\"post\">"; echo "<button type=\"submit\" />Remove</button><br />"; echo "</form>"; } } } So at this point Im not sure where to go from here for the remove button. Any suggestions would be appreciated.

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  • Letting users try your web app before sign-up: sessions or temp db?

    - by Mat
    I've seen a few instances now where web applications are letting try them out without you having to sign-up (though to save you need to of course). example: try at http://minutedock.com/ I'm wondering about doing this for my own web app and the fundamental question is whether to store their info into sessions or into a temp user table? The temp user table would allow logging and potentially be less of a hit on the server, correct? Is there a best practice here?

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  • Storing users in a database

    - by EMcKenna
    Im wondering whats the best way of storing different types of users in my database. I am writing an application that has 4 main user types (admin, school, teacher, student). At the moment I have a table for each of these but i'm not sure thats the best way of storing user information. For instance... Allowing students to PM other student is simple (store sender and receiver student_id) but enabling teachers to PM students requires another table (sender teacher_id, sender student_id). Should all users be stored in one users table with a user_type field? If so, the teacher / student specific information will still have to be stored in another table. users user_id, password_hash, user_type students user_id, student_specific_stuff... teachers user_id, teacher_specific_stuff... How do I stop a user who has a user_type = student from being accidentally being entered into the teachers table (as both have a user_id) Just want to make sure I get the database correct before i go any further. Thanks...

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  • How do I get the median/mode/range of a column in SQL using Java?

    - by Derek
    I have to get the median, mode and range of test scores from one column in a table but I am unsure how to go about doing that. When you connect to the database using java, you are normally returned a ResultSet that you can make a table or something out of but how do you get particular numbers or digits? Is there an SQL command to get the median/mode/range or will I have to calculate this myself, and how do you pull out numbers from the table in order to be able to calculate the mode/median/range? Thanks.

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  • Database Design Question

    - by deniz
    Hi, I am designing a database for a project. I have a table that has 10 columns, most of them are used whenever the table is accessed, and I need to add 3 more rows; View Count Thumbs Up (count) Thumbs Down (Count) which will be used on %90 of the queries when the table is accessed. So, my question is that whether it is better to break the table up and create new table which will have these 3 columns + Foreign ID, or just make it 13 columns and use no joins? Since these columns will be used frequently, I guess adding 3 more columns is better, but if I need to create 10 more columns which will be used %90 of the time, should I add them as well, or create a new table and use joins? I am not sure when to break the table if the columns are used very frequently. Do you have any suggestions? Thanks in advance,

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  • Loading .sql files from within PHP

    - by Josh Smeaton
    I'm creating an installation script for an application that I'm developing and need to create databases dynamically from within PHP. I've got it to create the database but now I need to load in several .sql files. I had planned to open the file and mysql_query it a line at a time - until I looked at the schema files and realised they aren't just one query per line. So, please.. how do I load an sql file from within PHP? (as phpMyAdmin does with it's import command).

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  • Search a string to find which records in table are inside said string

    - by Improfane
    Hello, Say I have a string. Then I have a number of unique tokens or keywords, potentially a large number in a database. I want to search and find out which of these database strings are inside the string I provide (and get the IDs of them). Is there a way of using a query to search the provided string or must it be taken to application space? Am I right in thinking that this is not a 'full text search'? Would the best method be to insert it into the database to make it a full text search?

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  • Error occure while validating form input using JQUERY in Firebug

    - by Param-Ganak
    Hello Friends, I have written a custom validation code in JQUERY. which is working fine. I have a login form which have two fields i.e. userid and password. I have written a custom JQUERY code for client side validation for these fields. This custom JQUERY code is working fine and gives me proper error messages as per the situation. But the problem with this code is that when I enter the invalid data in any or both field and press submit button of form then it displays the proper error message but at the same time when I checked it in Firebug it displays following error message when submit button of the form is clicked validate is not defined function onclick(event) { javascript: return validate(); }(click clientX=473, clientY=273) So please tell me where is I am wrong in my Jquery code. Thank You!

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  • Could someone give me their two cents on this optimization strategy

    - by jimstandard
    Background: I am writing a matching script in python that will match records of a transaction in one database to names of customers in another database. The complexity is that names are not unique and can be represented multiple different ways from transaction to transaction. Rather than doing multiple queries on the database (which is pretty slow) would it be faster to get all of the records where the last name (which in this case we will say never changes) is "Smith" and then have all of those records loaded into memory as you go though each looking for matches for a specific "John Smith" using various data points. Would this be faster, is it feasible in python, and if so does anyone have any recommendations for how to do it?

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  • Product Name Print Several times, How to fix.?

    - by mans
    i had added the following Opencart module for my order report list... http://www.opencart.com/index.php?route=extension/extension/info&extension_id=3597&filter_search=order%20list%20filter%20model&page=4 I have problems with the column "Products". If there are more than one option the products name prints several times. So if I got a product with three options the product name prints three times. Is there any way to fix this problem? i want print product name and model number only once, any idea.? i will attach the results what i got now... this is my sql query... public function getOrders($data = array()) { $sql = "select o.order_id,o.email,o.telephone,CONCAT(o.shipping_address_1, ' ', o.shipping_address_2) AS address,CONCAT(o.firstname, ' ', o.lastname) AS customer,o.payment_zone AS state,o.payment_address_2 AS block, o.payment_address_1 AS address,o.payment_postcode AS postcode,(SELECT os.name FROM " . DB_PREFIX . "order_status os WHERE os.order_status_id = o.order_status_id AND os.language_id = '" . (int)$this->config->get('config_language_id') . "') AS status,o.payment_city AS city,GROUP_CONCAT(pd.name) AS pdtname,GROUP_CONCAT(op.model) AS model,o.date_added,sum(op.quantity) AS quantity,GROUP_CONCAT(opt.value ) AS options, GROUP_CONCAT(opt.order_product_id ) AS ordprdid,GROUP_CONCAT(op.order_product_id ) AS optprdid, GROUP_CONCAT(op.quantity) AS opquantity from `" . DB_PREFIX . "order` o LEFT JOIN " . DB_PREFIX . "order_product op ON (op.order_id = o.order_id) LEFT JOIN " . DB_PREFIX . "product_description pd ON (pd.product_id = op.product_id and pd.language_id = '" . (int)$this->config->get('config_language_id') . "') LEFT JOIN " . DB_PREFIX . "order_option opt ON (opt.order_product_id = op.order_product_id) "; Product Name = GROUP_CONCAT(pd.name) AS pdtname,

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  • compile error: The import xxxx cannot be resolved

    - by Zachary
    I am developing a Java project using Eclipse. The project uses another project called engine, which I have added in my project build-path. As I need to call a dabo class, called House, in one of my project class, named Window, I have used the following code as usual: import ee.asus.kernel.House; I got however the following error in compiling time: Exception in thread "main" java.lang.Error: Unresolved compilation problems: The import ee cannot be resolved House cannot be resolved to a type House cannot be resolved to a type House cannot be resolved to a type at main.ee.asus.GUI.FrameWindow.Window.<init>(Window.java:10) at main.ee.asus.GUI.StartApplication.main(StartApplication.java:13) It's worth to point out that my prject and the dabo project use the same directory/packages names. Does anyone have a clue where the error may be?

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  • Killing the mysqld process

    - by Josh K
    I have a table with ~800k rows. I ran an update users set hash = SHA1(CONCAT({about eight fields})) where 1; Now I have a hung Sequel Pro process and I'm not sure about the mysqld process. This is two questions: What harm can possibly come from killing these programs? I'm working on a separate database, so no damage should come to other databases on the system, right? Assume you had to update a table like this. What would be a quicker / more reliable method of updating without writing a separate script. I just checked with phpMyAdmin and it appears as though the query is complete. I still have Sequel Pro using 100% of both my cores though...

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  • sql select with exact outcome

    - by Shiro
    Asking a simple question, just want everyone have fun to solve it. I got 2 tables. 1. Student 2. Course Student +----+--------+ | id | name | +----+--------+ | 1 | User1 | | 2 | User2 | +----+--------+ Course +----+------------+------------+ | id | student_id | course_name| +----+------------+------------+ | 1 | 1 | English | | 2 | 1 | Chinese | | 3 | 2 | English | | 4 | 2 | Japanese | +----+------------+------------+ I would like to get the result all student, who have taken English and Chinese, NOT English or Chinese. Expected result: +----+------------+------------+ | id | student_id | course_name| +----+------------+------------+ | 1 | 1 | English | | 2 | 1 | Chinese | +----+------------+------------+ What we normally do is select * from student join course on (student.id = course.student_id) WHERE course_name = 'English' OR course_name = 'Chinese' but in this result I can get User2 record which is not my expected result. I want the record only display the User take the course English+Chinese only.

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  • Resetting Objects vs. Constructing New Objects

    - by byronh
    Is it considered better practice and/or more efficient to create a 'reset' function for a particular object that clears/defaults all the necessary member variables to allow for further operations, or to simply construct a new object from outside? I've seen both methods employed a lot, but I can't decide which one is better. Of course, for classes that represent database connections, you'd have to use a reset method rather than constructing a new one resulting in needless connecting/disconnecting, but I'm talking more in terms of abstraction classes. Can anyone give me some real-world examples of when to use each method? In my particular case I'm thinking mostly in terms of ORM or the Model in MVC. For example, if I would want to retrieve a bunch of database objects for display and modify them in one operation.

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  • selecting data from table based on date .

    - by mehdi
    i have database table like this +-------+--------------+----------+ | id | ip | date | +-------+--------------+----------+ | 505 |192.168.100.1 |2010-04-03| | 252 |192.168.100.5 |2010-03-03| | 426 |192.168.100.6 |2010-03-03| | 201 |192.168.100.7 |2010-04-03| | 211 |192.168.100.10|2010-04-03| +-------+--------------+----------+ how can i retirive data from this table where month=03 how to write sql to do that . select * from table where month=03 something like that .

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  • Form Not Submitting

    - by John
    Hello, When I try to click on the "submit" button for the form below, nothing happens. Any ideas why not? Thanks in advance, John submit.php: <?php require_once "header.php"; $u = $_SESSION['username']; if (!isLoggedIn()) { // user is not logged in. if (isset($_POST['cmdlogin'])) { // retrieve the username and password sent from login form & check the login. if (checkLogin($_POST['username'], $_POST['password'])) { show_userbox2(); } else { echo "Incorrect Login information !"; show_loginform(); } } else { show_loginform(); } } else { . show_userbox2(); } echo '<div class="submittitle">Submit an item.</div>'; echo '<form action="http://www...com/.../submit2.php" method="post"> <input type="hidden" value="'.$_SESSION['loginid'].'" name="uid"> <div class="submissiontitle"><label for="title">Story Title:</label></div> <div class="submissionfield"><input name="title" type="title" id="title" maxlength="1000"></div> <div class="urltitle"><label for="url">Link:</label></div> <div class="urlfield"><input name="url" type="url" id="url" maxlength="500"></div> <div class="submissionbutton"><input name="submit" type="submit" value="Submit"></div> </form> '; ?> submit2.php: <?php //if($_SERVER['REQUEST_METHOD'] == "POST"){header('Location: http://www...com/.../submit2.php');} require_once "header.php"; if (isLoggedIn() == true) { $remove_array = array('http://www.', 'http://', 'https://', 'https://www.', 'www.'); $cleanurl = str_replace($remove_array, "", $_POST['url']); $cleanurl = strtolower($cleanurl); $cleanurl = preg_replace('/\/$/','',$cleanurl); $title = $_POST['title']; //$url = $_POST['url']; $uid = $_POST['uid']; $title = mysql_real_escape_string($title); $cleanurl = mysql_real_escape_string($cleanurl); $site1 = 'http://' . $cleanurl; $displayurl = parse_url($site1, PHP_URL_HOST); function isURL($url1 = NULL) { if($url1==NULL) return false; $protocol = '(http://|https://)'; $allowed = '[-a-z0-9]{1,63}'; $regex = "^". $protocol . // must include the protocol '(' . $allowed . '\.)'. // 1 or several sub domains with a max of 63 chars '[a-z]' . '{2,6}'; // followed by a TLD if(eregi($regex, $url1)==true) return true; else return false; } if(isURL($site1)==true) mysql_query("INSERT INTO submission VALUES (NULL, '$uid', '$title', '$cleanurl', '$displayurl', NULL)"); else echo "<p class=\"topicu\">Not a valid URL.</p>\n"; } else { // user is not loggedin show_loginform(); } if (!isLoggedIn()) { // user is not logged in. if (isset($_POST['cmdlogin'])) { // retrieve the username and password sent from login form & check the login. if (checkLogin($_POST['username'], $_POST['password'])) { show_userbox(); } else { echo "Incorrect Login information !"; show_loginform(); } } else { // User is not logged in and has not pressed the login button // so we show him the loginform show_loginform(); } } else { // The user is already loggedin, so we show the userbox. show_userbox(); } require_once "footer.php"; ?>

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  • How to join nearly identical several queries into one?

    - by Devyn
    Hi, Assume I have an order_dummy table where order_dummy_id, order_id, user_id, book_id, author_id are stored. You may complain the logic of my table but I somehow need to do it that way. I want to execute following queries. SELECT * FROM order_dummy WHERE order_id = 1 AND user_id = 1 AND book_id = 1 ORDER BY `order_dummy_id` DESC LIMIT 1 SELECT * FROM order_dummy WHERE order_id = 1 AND user_id = 1 AND book_id = 2 ORDER BY `order_dummy_id` DESC LIMIT 1 SELECT * FROM order_dummy WHERE order_id = 1 AND user_id = 1 AND book_id = 3 ORDER BY `order_dummy_id` DESC LIMIT 1 Please keep in mind that several numbers of same book is included in one order. Therefore, I list order_dummy_id by descending and limit 1 so only LATEST ORDER of A BOOK is shown. But my goal is to show other books in that way in one table. I used group by like this ... SELECT * FROM order_dummy WHERE order_id = 1 AND user_id = 1 GROUP BY book_id but it only shows order_dummy_id with ascending result. I have no idea anymore. Looking forward your kindness help!

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