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  • SQL SERVER – Curious Case of Disappearing Rows – ON UPDATE CASCADE and ON DELETE CASCADE – Part 1 of 2

    - by pinaldave
    Social media has created an Always Connected World for us. Recently I enrolled myself to learn new technologies as a student. I had decided to focus on learning and decided not to stay connected on the internet while I am in the learning session. On the second day of the event after the learning was over, I noticed lots of notification from my friend on my various social media handle. He had connected with me on Twitter, Facebook, Google+, LinkedIn, YouTube as well SMS, WhatsApp on the phone, Skype messages and not to forget with a few emails. I right away called him up. The problem was very unique – let us hear the problem in his own words. “Pinal – we are in big trouble we are not able to figure out what is going on. Our product details table is continuously loosing rows. Lots of rows have disappeared since morning and we are unable to find why the rows are getting deleted. We have made sure that there is no DELETE command executed on the table as well. The matter of the fact, we have removed every single place the code which is referencing the table. We have done so many crazy things out of desperation but no luck. The rows are continuously deleted in a random pattern. Do you think we have problems with intrusion or virus?” After describing the problems he had pasted few rants about why I was not available during the day. I think it will be not smart to post those exact words here (due to many reasons). Well, my immediate reaction was to get online with him. His problem was unique to him and his team was all out to fix the issue since morning. As he said he has done quite a lot out in desperation. I started asking questions from audit, policy management and profiling the data. Very soon I realize that I think this problem was not as advanced as it looked. There was no intrusion, SQL Injection or virus issue. Well, long story short first - It was a very simple issue of foreign key created with ON UPDATE CASCADE and ON DELETE CASCADE.  CASCADE allows deletions or updates of key values to cascade through the tables defined to have foreign key relationships that can be traced back to the table on which the modification is performed. ON DELETE CASCADE specifies that if an attempt is made to delete a row with a key referenced by foreign keys in existing rows in other tables, all rows containing those foreign keys are also deleted. ON UPDATE CASCADE specifies that if an attempt is made to update a key value in a row, where the key value is referenced by foreign keys in existing rows in other tables, all of the foreign key values are also updated to the new value specified for the key. (Reference: BOL) In simple words – due to ON DELETE CASCASE whenever is specified when the data from Table A is deleted and if it is referenced in another table using foreign key it will be deleted as well. In my friend’s case, they had two tables, Products and ProductDetails. They had created foreign key referential integrity of the product id between the table. Now the as fall was up they were updating their catalogue. When they were updating the catalogue they were deleting products which are no more available. As the changes were cascading the corresponding rows were also deleted from another table. This is CORRECT. The matter of the fact, there is no error or anything and SQL Server is behaving how it should be behaving. The problem was in the understanding and inappropriate implementations of business logic.  What they needed was Product Master Table, Current Product Catalogue, and Product Order Details History tables. However, they were using only two tables and without proper understanding the relation between them was build using foreign keys. If there were only two table, they should have used soft delete which will not actually delete the record but just hide it from the original product table. This workaround could have got them saved from cascading delete issues. I will be writing a detailed post on the design implications etc in my future post as in above three lines I cannot cover every issue related to designing and it is also not the scope of the blog post. More about designing in future blog posts. Once they learn their mistake, they were happy as there was no intrusion but trust me sometime we are our own enemy and this is a great example of it. In tomorrow’s blog post we will go over their code and workarounds. Feel free to share your opinions, experiences and comments. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Should all foreign table references use foreign key constraints

    - by TecBrat
    Closely related to: Foreign key restrictions -> yes or no? I asked a question on SO and it led me to ask this here. If I'm faced with a choice of having a circular reference or just not enforcing the restraint, which is the better choice? In my particular case I have customers and addresses. I want an address to have a reference to a customer and I want each customer to have a default billing address id and a default shipping address id. I might query for all addresses that have a certain customer ID or I might query for the address with the ID that matches the default shipping or billing address ids. I'm not sure yet how the constraints (or lack of) will effect the system as my application and it's data age.

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  • Having a generic data type for a database table column, is it "good" practice?

    - by Yanick Rochon
    I'm working on a PHP project where some object (class member) may contain different data type. For example : class Property { private $_id; // (PK) private $_ref_id; // the object reference id (FK) private $_name; // the name of the property private $_type; // 'string', 'int', 'float(n,m)', 'datetime', etc. private $_data; // ... // ..snip.. public getters/setters } Now, I need to perform some persistence on these objects. Some properties may be a text data type, but nothing bigger than what a varchar may hold. Also, later on, I need to be able to perform searches and sorting. Is it a good practice to use a single database table for this (ie. is there a non negligible performance impact)? If it's "acceptable", then what could be the data type for the data column?

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  • Jokes search engine / PHP based search engine on database

    - by matt74tm
    I'm looking for a script, functioning like the Google homepage that fetches data from a database rather than the internet. This is not intended to be a search engine, but a repository of jokes that can be pulled depending on the keywords typed. No sophisticated search techniques are required - keyword based is perfectly fine. If some mechanism of up/down-voting jokes can be incorporated, that would be fantastic, but I'm presuming that will be an entirely different game.

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  • Almost Realtime Data and Web application

    - by Chris G.
    I have a computer that is recording 100 different data points into an OPC server. I've written a simple OPC client that can read all of this data. I have a front-end website on a different network that I would like to consume this data. I could easily set the OPC client to send the data to a SQL server and the website could read from it, but that would be a lot of writes. If I wanted the data to be updated every 10 seconds I'd be writing to the database every 10 seconds. (I could probably just serialize the 100 points to get 1 write / 10 seconds but that would also limit my ability to search the data later). This solution wouldn't scale very well. If I had 100 of these computers the situation would quickly grow out of hand. Obviously I am well out of my league here and I have no experience with working with a large amount of data like this. What are my options and what should I research?

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  • Breaking up a large PHP object used to abstract the database. Best practices?

    - by John Kershaw
    Two years ago it was thought a single object with functions such as $database->get_user_from_id($ID) would be a good idea. The functions return objects (not arrays), and the front-end code never worries about the database. This was great, until we started growing the database. There's now 30+ tables, and around 150 functions in the database object. It's getting impractical and unmanageable and I'm going to be breaking it up. What is a good solution to this problem? The project is large, so there's a limit to the extent I can change things. My current plan is to extend the current object for each table, then have the database object contain these. So, the above example would turn into (assume "user" is a table) $database->user->get_user_from_id($ID). Instead of one large file, we would have a file for every table.

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  • 1 to 1 Comparison and Ranking System

    - by David
    I'm looking to create a comparison and ranking system which allows users to view 2 items, click on the one that they feel is the better one and then get presented with 2 more random items and continue to do this until they decide to stop. In the background, I want the system to use these wins and loses to rank each item in an overall ranking table so I can then see what is #1 and what isn't. I haven't got a clue where to begin with the formula, but I image I need to log wins and loses. Any help/direction appreciated!

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  • Jokes search engine / PHP based search engine on database

    - by matt_tm
    I'm looking for a script, functioning like the Google homepage that fetches data from a database rather than the internet. This is not intended to be a search engine, but a repository of jokes that can be pulled depending on the keywords typed. No sophisticated search techniques are required - keyword based is perfectly fine. If some mechanism of up/down-voting jokes can be incorporated, that would be fantastic, but I'm presuming that will be an entirely different game.

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  • Architecture for a site "blog"/"news reel"

    - by DavidScherer
    I really don't want to undertake handling blog/news posts within a site I'm working on and would much rather use some other software that's fairly bare-bones that will manage the posts and then I can just pull posts from the DB or an API. Does anyone have any experience with a nice, lightweight OS Blog type software that has either an API or is basic enough to simply pull Data from the database? I really only need the software for managing, I plan to display all the posts programatically through MVC.

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  • Good way to manage blog/news? [closed]

    - by DavidScherer
    I really don't want to undertake handling blog/news posts within a site I'm working on and would much rather use some other software that's fairly bare-bones that will manage the posts and then I can just pull posts from the DB or an API. Does anyone have any experience with a nice, lightweight OS Blog type software that has either an API or is basic enough to simply pull Data from the database? I really only need the software for managing, I plan to display all the posts programatically through MVC.

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  • Data base structure of a subscriber list

    - by foodil
    I am building a application that allow different user to store the subscriber information To store the subscriber information , the user first create a list For each list, there is a ListID. Subscriber may have different attribute : email phone fax .... For each list, their setting is different , so a require_attribute table is introduced. It is a bridge between subscriber and List That store Listid ,subid , attribute, datatype That means the system have a lot of list, each user have their own list, and the list have different attribute, some list have email , phone , some may have phone, address, name mail.. And the datatype is different, some may use 'name' as integer , some may use 'name' as varchar attribute means email phone, it is to define for which list have which subscriber attribute datatype means for each attribute, what is its datatype Table :subscriber : Field :subid , name,email Table :Require Attribute: Field : Listid ,subid , attribute, datatype The attribute here is {name, email} So a simple data is Subscriber: 1 , MYname, Myemail Require Attribute : Listid , 1 , 'email', 'intger' Listid , 1 , 'name', 'varchar' I found that this kind of storage is too complex too handle with, Since the subscriber is share to every body, so if a person want to change the datatype of name, it will also affect the data of the other user. Simple error situation: Subscriber: list1, Subscriber 1 , name1, email1 list2, Subscriber 2 , name2 , email2 Require Attribute : List1 , Subscriber 1 , 'email', 'varchar', List1 , Subscriber 1 , 'name', 'varchar', Listid , Subscriber 2 , 'email', 'varchar', Listid , Subscriber 2, 'name', 'integer', if user B change the data type of name in require attribute from varchar to integer, it cause a problem. becasue list 1 is own by user A , he want the datatype is varchar, but list 2 is won by user B , he want the datatype to be integer So how can i redesign the structure?

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  • What is the disadvantage of using abstract class as a database connectivity in zend framework 2 instead of service locator

    - by arslaan ejaz
    If I use database by creating adapter with drivers, initialize it in some abstract class and extend that abstract class to required model. Then use simple query statement. Like this: namespace My-Model\Model\DB; abstract class MysqliDB { protected $adapter; public function __construct(){ $this->adapter = new \Zend\Db\Adapter\Adapter(array( 'driver' => 'Mysqli', 'database' => 'my-database', 'username' => 'root', 'password' => '' )); } } And use abstract class of database like this in my models: class States extends DB\MysqliDB{ public function __construct(){ parent::__construct(); } protected $states = array(); public function select_all_states(){ $data = $this->adapter->query('select * from states'); foreach ($data->execute() as $row){ $this->states[] = $row; } return $this->states; } } I am new to zend framework, before i have experience of working in YII and Codeigniter. I like the object oriented in zend so i want to use it like this. And don't want to use it through service locater something like this: public function getServiceConfig(){ return array( 'factories' => array( 'addserver-mysqli' => new Model\MyAdapterFactory('addserver-mysqli'), 'loginDB' => function ($sm){ $adapter = $sm->get('addserver-mysqli'); return new LoginDB($adapter); } ) ); } In module. Am i Ok with this approach?

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  • How can I get my mysqld-swamped CPU under control?

    - by Shay Guy
    I was AFK for about 24 hours and came back to find gnome-system-monitor saying all four CPU cores on my laptop were running at full throttle. mysqld is taking up more than one full core; when I tried to end the process, it restarted with a new PID. Then there's ksoftirqd/0-3, which apparently has something to do with interrupts, but I can't tell from Google what I'm supposed to do with those four particular processes. They're taking up a quarter or more of my processor cycles. Then there's Chrome, but I can probably handle that on my own -- how do I cool down the other processes giving me problems?

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  • Fetching database query through function

    - by Shubham Maurya
    I am sick of connecting database in each script i need a more OOP approach to fetching database results. ex like wordpress use wpdb class to fetch results. This what wordpress does to get data <?php $posts = $wpdb->get_results("SELECT ID, post_title FROM $wpdb->posts WHERE post_status = 'publish' AND post_type='post' ORDER BY comment_count DESC LIMIT 0,4") ?> How can i create the same feature too using any class or function and use it in my script Thank you

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  • Storing User-uploaded Images

    - by Nyxynyx
    What is the usual practice for handling user uploaded photos and storing them on the database and server? For a user profile image: After receiving the image file from user, rename file to <image_id>_<username> Move image to /images/userprofile Add img filename to a table users containing their profile details like first_name, last_name, age, gender, birthday For a image for a review done by user: After receiving the image file from user, rename file to <image_id>_<review_id> Move image to /images/reviews Add img filename to a table reviews containing their profile details like review_id, review_content, user_id, score. Question 1: How should I go about storing the image filenames if the user can upload multiple photos for a particular review? Serialize? Question 2: Or have another table review_images with columns review_id, image_id, image_filename just for tracking images? Will doing a JOIN when retriving the image_filename from this table slow down performance noticeably? Question 3: Should all the images be stored in a single folder? Will there be a problem when we have 100K photos in the same folder? Is there a more efficient way to go about doing this?

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  • XMLHttpRequest not working, trying to test database connection [closed]

    - by Frederick Marcoux
    I'm currently creating my own CMS for personnal use but I'm blocked at a code. I'm trying to make a installation script but the AJAX request to test if database works, doesn't work... There's my JS code: function testDB() { "use strict"; var host = document.getElementById('host').value; var username = document.getElementById('username').value; var password = document.getElementById('password').value; var db = document.getElementById('db_name').value; var xmlhttp = new XMLHttpRequest(); var url = "test_db.php"; var params = "host="+host+"&username="+username+"&password="+password+"&db="+db; xmlhttp.open("POST", url, true); xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded"); xmlhttp.setRequestHeader("Content-length", params.length); xmlhttp.setRequestHeader("Connection", "close"); xmlhttp.send(params); $('#loader').removeAttr('style'); if (xmlhttp.responseText !== '') { if (xmlhttp.readyState===4 && xmlhttp.status===200) { $('#next').removeAttr('disabled'); $('#test').attr('disabled', 'disabled'); $('#test').text('Connection Successful!'); $('#test').addClass('btn-success'); $('#login').addClass('success'); $('#login1').addClass('success'); $('#db').addClass('success'); $('#loader').attr('style', 'display: none;'); } else { $('#next').attr('disabled', 'disabled'); $('#test').removeClass('btn-success'); $('#test').removeAttr('disabled'); $('#test').text('Test Connection'); $('#login').removeClass('success'); $('#login1').removeClass('success'); $('#db').removeClass('success'); $('#loader').attr('style', 'display: none;'); } } else { $('#next').attr('disabled', 'disabled'); $('#next').attr('disabled', 'disabled'); $('#test').removeClass('btn-success'); $('#test').removeAttr('disabled'); $('#test').text('Test Connection'); $('#login').removeClass('success'); $('#login1').removeClass('success'); $('#db').removeClass('success'); $('#loader').attr('style', 'display: none;'); } } And there's my PHP code: <?php $link = mysql_connect($_POST['host'], $_POST['username'], $_POST['password']); if (!$link) { echo ''; } else { if (mysql_select_db($_POST['db'])) { echo 'Connection Successful!'; } else { echo ''; } } mysql_close($link); ?> I don't know why it doesn't work but I tried with JQuery $.ajax, $.get, $.post but nothing work...

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  • Unified data source for k2 installed Joomla websites

    - by Özkan ÖZLÜ
    I am responsible for a few web sites of my organization. I use Joomla! 2.5.9 for those web sites. They all are running at the same server. I use K2 component for content managing. I have a general website in which shows all the staff information at the 'Staff' page. Also some of those people and their contents are shown in another department's website. So, there are databases for each web site. For example: In the general website (let's say general.org), when I click on the 'Staff' menu item, page shows all of the people work at my organization. Also they work at different departments. In another web site (eg: education.general.org) when I click on the 'Staff' menu item, it shows the people work at education department. But for each web site, I have different user accounts which means a modification in one of them does not affect the other one. If the one of the education staff tries to change his profile picture on the education web site, he also has to do it on the general web site. And sometimes one person might be working at two departments. Thus he has to edit three times of his data. Is it possible to merge the records for all websites? In other words, I want everyone to insert/update their data on the general web site, and the other web sites will be updated automatically.

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  • How do I access column data in a previous select statement from a sub-query? [closed]

    - by payling
    PROBLEM How do I access column data in a previous select statement from a sub-query? Below is a simple mock up of what I'm attempting to do. Tables used: Quotes, Users QUOTES TABLE qid, (quote id) owner_uid, creator_uid SQL SYNTAX: SELECT q.qid, q.owner_uid, q.creator_uid, owner.fname, owner.lname FROM quotes q, (SELECT u.fname, u.lname FROM users u WHERE u.uid = q.owner_uid) AS owner WHERE q.qid = '#' SUMMARY I want to be able to use the quote table's owner_uid and specify it for the owner table so I can return all the owner info for that particular quote. The problem is, q.owner_uid is not recognized in the owner sub-query. What am I doing wrong?

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  • How to set permalink of your blog post according to date and title of post?

    - by Amit
    I am having this website http://www.finalyearondesk.com . My blogs post link are set like this.. http://www.finalyearondesk.com/index.php?id=28 . I want it to set like this ... finalyearondesk.com/2011/09/22/how-to-recover-ubuntu-after-it-is-crashed/ . I am using the following function to get these posts... function get_content($id = '') { if($id != ""): $id = mysql_real_escape_string($id); $sql = "SELECT * from blog WHERE id = '$id'"; $return = '<p><a href="http://www.finalyearondesk.com/">Go back to Home page</a></p>'; echo $return; else: $sql = "select * from blog ORDER BY id DESC"; endif; $res = mysql_query($sql) or die(mysql_error()); if(mysql_num_rows($res) != 0): while($row = mysql_fetch_assoc($res)) { echo '<h1><a href="index.php?id=' . $row['id'] . '">' . $row['title'] . '</a></h1>'; echo '<p>' . "By: " . '<font color="orange">' . $row['author'] . '</font>' . ", Posted on: " . $row['date'] . '<p>'; echo '<p>' . $row['body'] . '</p><br />'; } else: echo '<p>We are really very sorry, this page does not exist!</p>'; endif; } Any suggestions how to do this? And can we do this by using .htaccess?

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  • Else statement to show connection successful [closed]

    - by Craig Smith
    I am trying to write a script to test a database connection, at the moment it will only display text if the connection doesn't work, I am stuck with trying to create an else statement to display "Connection Successful" if it works. Here's my code so far. Any help appreciated :) <? $conn = @mysql_connect("localhost", "root", ""); if (!$conn) { die("Connection failed: " .mysql_error()); } ?>

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  • Should I encrypt data in database?

    - by Tio
    I have a client, for which I'm going to do an Web application about patient care, managing patients, consults, history, calendars, everything about that basically. The problem is that this is sensitive data, patient history and such. The client insists on encrypting the data at the database level, but I think this is going to deteriorate the performance of the web app. ( But maybe I shouldn't be worried about this ) I've read the laws about data protection on health issues ( Portugal ), but isn't very specific about this ( I just questioned them about this, I'm waiting for their response ). I've read the following link, but my question is different, should I encrypt the data in the database, or not. One problem that I foresee in encrypting data, is that I'm going to need a key, this could be the user password, but we all know how user passwords are ( 12345 etc etc ), and generating a key I would have to store it somewhere, this means that the programmer, dba, whatever could have access to it, any thoughts on this? Even adding an random salt to the user password isn't going to solve the problem since I can always access it, and therefore decrypt the data.

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  • Foreign key restrictions -> yes or no?

    - by This is it
    I would like to hear some”real life experience” suggestions if foreign key restrictions are good or bad thing to enforce in DB. I would kindly ask students/beginners to refrain from jumping and answering quickly and without thinking. At the beginning of my career I thought that stupidest thing you can do is disregard the referential integrity. Today, after "few" projects I'm thinking different. Quite different. What do you think: Should we enforce foreign key restrictions or not? *Please explain your answer.

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  • How to build completely modular web applications

    - by Webnet
    In the coming months we're going to begin a project where we take a system we've built for a client (v1) and rebuild it from scratch. Our goal with v2 is to make it modular, so that this specific client will have their own set of modules they use, then another client may use a different set of modules altogether. The trick here is that Company A might have a series of checkout and user modules that change how that system works. Company B might stick with the standard checkout procedure but customize how products are browsed. What are some good approaches to application architecture when you're building an application from scratch that you want to have a Core that's shared among all clients while still maintaining the flexability for anything to be modified specifically for a client? I've seen CodeIgniter's hooks and don't think that's a good solution as we could end up with 250 hooks and it's still not flexible enough. What are some other solutions? Ideally we won't need to draw a line in the sand.

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  • Dynamic Fields/Columns

    - by DanMark
    What is the best way to allow for dynamic fields/database columns? For example, let's say we have a payroll system that allows a user to create unique salary structures for each employee. How could/should one handle this scenario? I thought of using a "salary" table that hold the salary component fields and joining these columns to a "salary_values" table that hold the actual values. Does this make sense? Example Salary Structures: Notice how the components of the salary can be shared or unique. -- Jon's Salary -- Basic 100 Annual Bonus 25 Tel. Allowances 15 -- Jane's Salary -- Basic 100 Travel Allowances 10 Bi-annual Bonus 30

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  • Identifying elements from data feeds generated by affiliate sites

    - by SPI
    I am working with data feeds from affiliate sites. The basic idea is to provide an interface where the user can paste a link to an XML datafeed (these are huge btw, around 60 mb) that would then be streamed, parsed into small chunks, and mined for the required data which would then be stored in the database. The problem is that different affiliate sites have different Schemas for their XML's. It is a little hard mapping the elements in an XML to your database attributes when you don't actually know which element contains what. My Solution: Use XPath to traverse through the first set of parent and it's descendent's, fetch the elements as well as the data and and ask the user to map this data to the attributes in the database by selecting from a set of radio buttons that represent the attributes from the database. This will be done just once for each new Feed, once the system know's what's what it will automatically upload the data from the XML to the database. Does this sound viable? Is there a better solution? I realize this leaves an uncomfortable opening for human error.. Thanks.

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