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• MySQL - Calculating fields on the fly vs storing calculated data

  - by Christian Varga

  Hi Everyone, I apologise if this has been asked before, but I can't seem to find an answer to a question that I have about calculating on the fly vs storing fields in a database. I read a few articles that suggested it was preferable to calculate when you can, but I would just like to know if that still applies to the following 2 examples. Example 1. Say you are storing data relating to a car. You store the fuel tank size in litres, and how many litres it uses per 100km. You also want to know how many KMs it can travel, which can be calculated from the tank size and economy. I see 2 ways of doing this: When a car is added or updated, calculate the amount of KMs and store this as a static field in the database. Every time a car is accessed, calculate the amount of KMs on the fly. Because the cars economy/tank size doesn't change (although it could be edited), the KMs is a pretty static value. I don't see why we would calculate it every single time the car is accessed. Wouldn't this waste cpu time as opposed to simply storing it in a separate field in the database and calculating only when a car is added or updated? My next example, which is almost an entirely different question (but on the same topic), relates to counting children. Let's say we have a app which has categories and items. We have a view where we display all the categories, and a count of all the items inside each category. Again, I'm wondering what's better. To perform a MySQL query to count all the items in each category every single time the page is accessed? Or store the count in a field in the categories table and update when an item is added / deleted? I know it is redundant to store anything that can be calculated, but I worry that calculating fields or counting records might be slow as opposed to storing the data in a field. If it's not then please let me know, I just want to learn about when to use either method. On a small scale I guess it wouldn't matter either way, but apps like Facebook, would they really count the amount of friends you have every time someone views your profile or would they just store it as a field? I'd appreciate any responses to both of these scenarios, and any resource that might explain the benefits of calculating vs storing. Thanks in advance, Christian

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• What regular expression(s) would I use to remove escaped html from large sets of data.

  - by Elizabeth Buckwalter

  Our database is filled with articles retrieved from RSS feeds. I was unsure of what data I would be getting, and how much filtering was already setup (WP-O-Matic Wordpress plugin using the SimplePie library). This plugin does some basic encoding before insertion using Wordpress's built in post insert function which also does some filtering. I've figured out most of the filters before insertion, but now I have whacko data that I need to remove. This is an example of whacko data that I have data in one field which the content I want in the front, but this part removed which is at the end: <img src="http://feeds.feedburner.com/~ff/SoundOnTheSound?i=xFxEpT2Add0:xFbIkwGc-fk:V_sGLiPBpWU" border="0"></img> <img src="http://feeds.feedburner.com/~ff/SoundOnTheSound?d=qj6IDK7rITs" border="0"></img> &lt;img src=&quot;http://feeds.feedburner.com/~ff/SoundOnTheSound?i=xFxEpT2Add0:xFbIkwGc-fk:D7DqB2pKExk&quot; Notice how some of the images are escape and some aren't. I believe this has to do with the last part being cut off so as to be unrecognizable as an html tag, which then caused it to be html endcoded. Another field has only this which is now filtered before insertion, but I have to get rid of the others: &lt;img src=&quot;http://farm3.static.flickr.com/2183/2289902369_1d95bcdb85.jpg&quot; alt=&quot;post_img&quot; width=&quot;80&quot; (all examples are on one line, but broken up for readability) Question: What is the best way to work with the above escaped html (or portion of an html tag)? I can do it in Perl, PHP, SQL, Ruby, and even Python. I believe Perl to be the best at text parsing, so that's why I used the Perl tag. And PHP times out on large database operations, so that's pretty much out unless I wanted to do batch processing and what not. PS One of the nice things about using Wordpress's insert post function, is that if you use php's strip_tags function to strip out all html, insert post function will insert <p> at the paragraph points. Let me know if there's anything more that I can answer. Some article that didn't quite answer my questions. (http://stackoverflow.com/questions/2016751/remove-text-from-within-a-database-text-field) (http://stackoverflow.com/questions/462831/regular-expression-to-escape-html-ampersands-while-respecting-cdata)

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• How to convert full outer join query to O-R query?

  - by Kugel

  I'm converting relational database into object-relational in Oracle. I have a query that uses full outer join in the old one. Is it possible to write the same query for O-R database without explicitly using full outer join? For normal inner join it simple, I just use dot notation together with ref/deref. I'm interested in this in general so let's say the relational query is: select a.attr, b.attr from a full outer join b on (a.fk = b.pk); I want to know if it's a good idea to do it this way: select a.attr, b.attr from a_obj a full outer join b_obj b on (a.b_ref = ref(b));

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• How to use avg function?

  - by Marcelo

  I'm new at php and mysql stuff and i'm trying to use an avg function but i don't know how to. I'm trying to do something like this: mysql_connect(localhost,$username,$password); @mysql_select_db($database) or die ("Did not connect to $database"); mysql_query("AVG(column1) FROM table1 ") or die(mysql_error()); mysql_close(); echo AVG(column1); (Q1)I'd like to see the value printed in the screen, but i'm getting nothing but an error message. How could I print this average on the screen ? (Q2)If I had a column month in my table1, how could I print the averages by the months ? Sorry for any bad English, and thanks for the attention.

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• Read Call History from iPhone on iOS 5 and above

  - by Sandeep Dhama

  I am developing an application and need to read the users call history from iPhone.I have go though all the forums and google it and found that we can get the records from teh callHistory sqlite database by "private/var/root/Library/CallHistory/call_history.db". But this path is not working from iOS 5 and above. Seems like apple has changed all their database path and structure so that no one can accees it. I have also seen some of the application on iTunes who are capable of getting the users call history like:-https://itunes.apple.com/us/app/callog/id327883585?mt=8 I have also check a mac desktop utility called "WonderShare Dr.Fone" which will fetch all the data from your iPhone like call history messages, notes , etc.How this utility is fetching the call history records and other details? If their is any API or private APIs by which i can get the callHistory data path please let me know.

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• in c# how would one escape a break in quotes

  - by Derek Vance

  i am trying to database some files on my computer with mysql in c#, its having an issue with VALUES ('drum'n'bass')

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• Method of documentation for SQL Stored Procedures

  - by Chapso

  I work in a location where a single person is responsible for creating and maintaining all stored procedures for SQL servers, and is the conduit between software developers and the database. There are a lot of stored procedures in place, and with a database diagram it is simple enough 90% of the time to figure out what the stored procedure needs for arguments/returns as output. For the other 10% of the time, however, it would be helpful to have a reference. Since the DBA is a busy guy (aren't we all), it would be good to have some program which documents the stored procedures to a file so that the developers can see it without being able to access the SPs themselves. The question is, does anyone know of a good program to accomplish this? Basically what we need is something that gives the name of the SP, the argument list and the output, both with datatypes and a nullable flag.

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• PHP/MySQL - Special characters in URLs. How to avoid?

  - by RC

  Hey everyone, My database contains information extracted from an external feed. In this raw text feed, the following text is used in place of special characters: & - &amp; ' - &39; é - &eacute; I extract some of this text to form URLs. For example, a URL that I construct from data containing these characters might look like this: http://url.com/search/?brand=Franklin&Hédgson's I use the GET variables in this URL to construct further lookups, which leads to a couple of specific problems: The é and ' characters are sent back to MySQL as they appear, and so they don't trigger any results (because the characters take the full HTML form in the database text). The & within the URL separates the variable, and the GET returns only Franklin, when it should return the whole string. Are there any straightforward ways of dealing with this? Thanks.

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• Weird exception with OLEDB Parameter Insert

  - by Seamus MacKenzie

  Getting a strange error when trying to insert data into an Access database using parameters. the line where I am getting a problem is :- thisCommand.CommandText = "INSERT INTO Events (Venue_ID, Date_Start, Date_End, Time_Start, Time_End, Name, Description, Event_Type, Buy_Tickets_URL) VALUES (@VenID, @DStart, @DEnd, @evTime, @evTime, @Name, @Des, @EvType, @SysUrl);"; string desc = GetDesc(rec.EvName); thisCommand.Parameters.AddWithValue("@Des", desc); thisCommand.ExecuteNonQuery(); None of the other parameters cause a problem but when trying to insert data to the description field I get a database exception saying the field is too small to accept the amount of data. The problem is my program is only trying to insert 3 characters when it throws the error and the Description field is a memo so should be able to hold up to 65000+ characters. When inserting a value manually in the CommandText everything works fine so it must be something to do with the parameter properties.

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• Creating a pie chart for an app

  - by jhodgson4

  I'm developing an app which requires a pie chart to display a set number of modules. The modules need to be clickable, sending a value to the database for how many times the module has been clicked. The slices will change color etc depending on this database value. The slices will always be equal in size. All simple stuff. My question is what charting system would you use. I've been looking at google charts but I have no way of registering a value in a slice without changing its 'weight' in the chart. So ideally I would like to add data-stage="2" to each slice that I can access with a custom method. Also google charts seems quite heavy for what I need? Any advice would be greatly appreciated. Joe

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• Problem With Inserts of multibyte (converted to utf-8) strings in the mysql tables of utf_unicode_ci encoding

  - by user381595

  http://domainsoutlook.com/sandbox/keyword/?s=http://bhaskar.com raw example of my keyword density analyser. Every keyword shows up properly with no problems in unicode conversions etc. Now, When I am adding these words to the database column of a table, the words show up as messed up. http domainsoutlook.com/b/site/bhaskar.com.html For example on this front end page if you see there is a keyword that is shown as a blank but still occurs on the website 8 times. (It isnt empty in the database though). I have checked and there is no problem with mysql_real_escape_String...because the output stays the same before and after the word is gone through mysql_real_escape_String. Another problem was that I wanted to fix my urls for arabic language. They should be showing up as /word-{1st letter of the word}/{whole word}.html but its showing as /word-{whole word}/{1st letter of the word}.html I really need answers for these two questions.

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• Either .each do or .all isn't working how I think it should

  - by user1299656

  So whenever someone rates a shop, I want the Shop model to calculate its new average rating and store that in the database (instead of calculating the average every time someone looks at it). So I wrote the segment of code that follows, and it doesn't work. The loop always iterates exactly once, no matter how many shop_ratings in the database exist that have the shop's id as their shop_id. I played around with it a bit and found that every time a new rating is submitted the function is called successfully, but it only runs the loop once and sets the average to what the first rating was. I don't know if the "query" that sets the ratings variable is wrong or if it's the loop that's wrong. class Shop < ActiveRecord::Base has_many :shop_ratings attr_accessible :name, :latitude, :longitude validates_presence_of :name validates_presence_of :latitude validates_presence_of :longitude def distance_to(lat, long) return (self.longitude - long) + (self.latitude - lat) end def find_average total = 0 count = 0 ratings = ShopRating.all(:conditions => {:shop_id => id}) ratings.each do |submission| total = total + submission.rating count = count + 1 end update_attribute :average_rating, total/count end end

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• Send Email Using Classic ASP with an Embeded Image

  - by Khilen

  hi i am making NewsLetter using the wysiwyg Editor.. it allows me to upload the Image Path and Image Path is stored in the Upload Directory.. Not When i retrieve that Image using it works in website.. the editor's value is stored in database example <br> hi <img src="upload/acb.gif"> <br> Hello i am sending Email and the detail of this email is received from database and this detail is sent to visitor he is gettion all text value but not able to see Image so suggest me what to do..?

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• InnoDB not supported by webhost. What now?

  - by Peter Perhác

  I was developing a small WAMP web application on my laptop, where I have an instance of mySQL running and I chose InnoDB for my DB engine. After several weeks' development I wanted to make it available to the public and found out the database server provided by my web host does not support InnoDB, only MyISAM. The create-and-populate script generated from the innoDB schema on my laptop, when executed against the live database, can manage to create individual TABLES but then runs into problems creating the VIEWs. Are views not supported in MyISAM? I know FOREIGN KEYs are not. That's very much why I made the choice of InnoDB... What are my chances of making my innoDB schema design work with myISAM? Is there any straightforward way of converting the whole schema from one storage engine to the other? Should I look for another web host that does provide a mysql db that supports innoDB?

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• SQLite SQLite column can't be updated to any value but zero (real type)

  - by user1065320

  Hi I'm trying to create a three fields table (date,text,real), I can insert and update the first two fields but can't set or update the last one. createSQL = @"CREATE TABLE IF NOT EXISTS ACTIVITIES (MYDATE DATETIME PRIMARY KEY, ACTIVITY TEXT , LENGTH REAL);"; try to insert char *update = "INSERT OR REPLACE INTO ACTIVITIES (MYDATE, ACTIVITY , LENGTH) VALUES (?, ? ,?);"; sqlite3_stmt *stmt; if (sqlite3_prepare_v2(database, update , -1, &stmt, nil) == SQLITE_OK) { sqlite3_bind_double(stmt, 1, valueToWrite); sqlite3_bind_text(stmt, 2, [task UTF8String], -1, NULL); sqlite3_bind_double(stmt, 3, 1.5); } if (sqlite3_step(stmt) != SQLITE_DONE) { NSAssert1(0, @"Error updating table: %s", errorMsg); } sqlite3_finalize(stmt); sqlite3_close(database); The first two values are updated but the last one remains 0 even if I'm writing a value like 1.5 or put a double variable with a different value Thanks

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• sql server 2008 multiple inserts over 2 tables

  - by Rob

  I got the following trigger on my sql server 2008 database CREATE TRIGGER tr_check_stoelen ON Passenger AFTER INSERT, UPDATE AS BEGIN IF EXISTS( SELECT 1 FROM Passenger p INNER JOIN Inserted i on i.flight= p.flight WHERE p.flight= i.flightAND p.seat= i.seat ) BEGIN RAISERROR('Seat taken!',16,1) ROLLBACK TRAN END END The trigger is throwing errors when i try to run the query below. This query i supposed to insert two different passengers in a database on two different flights. I'm sure both seats aren't taken, but i can't figure out why the trigger is giving me the error. Does it have to do something with correlation? INSERT INTO passagier VALUES (13392,5315,3,'Janssen Z','2A','October 30, 2006 10:43','M'), (13333,5316,2,'Janssen Q','2A','October 30, 2006 11:51','V')

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• Gujarati Font Rendering

  - by Vishal Khakhkhar

  I am having sqlite database containing gujarati words.. The sql query for the database is... BEGIN TRANSACTION; CREATE TABLE eng_guj (_id INTEGER PRIMARY KEY, eng_word , guj_word ); INSERT INTO eng_guj VALUES(1,'aardvark','??? ??????? ?????????? ?? ?????? ????? ??????.'); COMMIT; I want to display the text in textview.. but its not rendering properly.. meant Its displaying the word in gujarati like "???????" will be displayed as "??????". I already have used Typeface and different ttf fonts.

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• How do I set up a test duplicate of a Django and Postgresql based web application?

  - by cojadate

  Not sure if this is an excessively broad and newbie-ish question for Stack Overflow but here goes: I paid someone else to build a web application for me and now I want to tweak certain aspects of it myself. I learn best by trial and error – changing stuff and seeing what happens. Obviously that's not a great way to treat a live site, so I need to duplicate the site on some kind of test server which I can play with without fear of the consequences. Unfortunately the closest I've come to programming has been creating ActionScript-based websites. I've never touched a database. So I really don't know where to start with setting up a test server. I would really appreciate any advice about where to start. I am completely ignorant and lost here. The web application is built in python/django using a Postgresql database. I use Mac OS X 10.6 if that makes any difference.

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• Trying to verify understanding of Foreign Keys MSSQL

  - by msarchet

  So I'm working on just a learning project to expose myself to doing some things I do not get to do at work. I'm just making a simple bug and case tracking app (I know there are a million this is just to work with some tools I don't get to). So I was designing my database and realized I've never actually used Foreign Keys before in any of my projects, I've used them before but never actually setting up a column as a FK. So I've designed my database as follows, which I think is close to correct (at least for the initial layout). However When I try to add the FK's to the linking Tables I get an error saying, "The tables present in the relationship must have the same number of columns". I'm doing this by in SQLSMS by going to the Keys 'folder' and adding a FK. Is there something that I am doing wrong here, I don't understand why the tables would have to have the same number of columns for me to add a FK relationship between the tables?

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• Mobile App integrating with Web portal

  - by Shine

  I'm planning to develop a city info site. The web pages will display contents from a constantly updating MySQL database- most probably using a CMS. I am planning to share the same database for a Mobile app related to this. In the pages there are options for using geolocation, rate and comment for the user. I think, this mobile app should work while it's offline too. So how should i deal with data for mobile? Should i use a connection between MySQL and IndexedDB? (I'm not quite sure about this part). Appreciating your time & help.

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• how much time it will take to learn action script 3 in flash

  - by Mirage

  I know php mysql , javascript , jquery very well. I have never touced flash. Now have to do website in complete flash with action scripting. Keeping flash animation and scripting separate. How much time it will take for me to build e,g 1)Simple page with 1 column layout like , header , navigation bar , content. 2)The navigation items will be loaded from database using xml and flash 3)The content will also load from database depending upon navigation item clicked HOw much time forinserting flash objects and how much time for scripting. Thanks

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• Can you hide tables from a MySQL user in phpMyAdmin?

  - by AK

  I have a MySQL user added to a database that I would like to prevent from viewing certain tables. I can limit their privileges through MySQL by preventing them from running statements like DROP or ALTER. But is it possible to prevent them from viewing certain tables in phpMyAdmin? If there isn't a MySQL privilege that controls this (I wouldn't imagine there would be), is there a configuration in phpMyAdmin that allows this? I understand one workaround here is to move the tables to a new database that they're not added to. This isn't an option for my application.

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• Huge page buffer vs. multiple simultaneous processes

  - by Andrei K.

  One of our customer has a 35 Gb database with average active connections count about 70-80. Some tables in database have more than 10M records per table. Now they have bought new server: 4 * 6 Core = 24 Cores CPU, 48 Gb RAM, 2 RAID controllers 256 Mb cache, with 8 SAS 15K HDD on each. 64bit OS. I'm wondering, what would be a fastest configuration: 1) FB 2.5 SuperServer with huge buffer 8192 * 3500000 pages = 29 Gb or 2) FB 2.5 Classic with small buffer of 1000 pages. Maybe some one has tested such case before and will save me days of work :) Thanks in advance.

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• Table character encoding - exception in application

  - by zgnilec

  I have a code: CREATE TABLE IF NOT EXISTS Person ( name varchar(24) ... ) CHARACTER SET utf8 COLLATE utf8_polish_ci; This works OK in my application, but I read if someone put in name field a string that contains character wchich code is greater than 127, database will use 2 bytes (or more) to store this character. So i think, i will change character set to utf16: CHARACTER SET utf16 COLLATE utf16_polish_ci; But now when I run my application, exception apears: KeyNotFoundException. It apears exactly at these instructions: MySqlCommand komenda = baza.Polaczenie.CreateCommand (); komenda.CommandText = zapytanie; MySqlDataReader dr = komenda.ExecuteReader (); // HERE, at execute reader method if (dr.Read ()) ... 1) Anyone had similar problem? 2) Any idea how to use always 2 bytes/char in database field?

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• How to write a datatable to excel work book at client side

  - by senthilkumar

  Hi Guys Currently i am doing one project in that we need to generate report from database. Since my server memory is too low im getting 'Out of Memory' Exception when im writing it at serverside and also when i write directly to a excel file using http header as excel file im not able to create multiple sheets since my database table is huge more than 65536 rows. I saw many solution using a third party tool but i cant use those into mine..If anyone already worked on this please give me some direction. Also i tried using javascript but for that i need to use datagrid at server side?? but in my project i m not allowed to use like this.

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