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  • SQL - First row inserted every day for the past X days

    - by okie.floyd
    A tough SQL question (I'm using postgres by the way). I need the first row inserted every day for the past X days. one of my columns is a timestamp, which i hold the time inserted, and another column is the row id. If it's not possible to get the first row inserted every day, i at least need a unique one; a single row for every day for the past x days. Any suggestions? Thanks okie

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  • Composite Primary and Cardinality

    - by srini.venigalla
    I have some questions on Composite Primary Keys and the cardinality of the columns. I searched the web, but did not find any definitive answer, so I am trying again. The questions are: Context: Large (50M - 500M rows) OLAP Prep tables, not NOSQL, not Columnar. MySQL and DB2 1) Does the order of keys in a PK matter? 2) If the cardinality of the columns varies heavily, which should be used first. For example, if I have CLIENT/CAMPAIGN/PROGRAM where CLIENT is highly cardinal, CAMPAIGN is moderate, PROGRAM is almost like a bitmap index, what order is the best? 3) What order is the best for Join, if there is a Where clause and when there is no Where Clause (for views) Thanks in advance.

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  • How many colunms in table to keep? - MySQL

    - by Dennis
    I am stuck between row vs colunms table design for storing some items but the decision is which table is easier to manage and if colunms then how many colunms are best to have? For example I have object meta data, ideally there are 45 pieces of information (after being normalized) on the same level that i need to store per object. So is 45 colunms in a heavry read/write table good? Can it work flawless in a real world situation of heavy concurrent read/writes?

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  • iPhone - Create non-persistent entities in core data

    - by ncohen
    Hi everyone, I would like to use entity objects but not store them... I read that I could create them like this: myElement = (Element *)[NSEntityDescription insertNewObjectForEntityForName:@"Element" inManagedObjectContext:managedObjectContext]; And right after that remove them: [managedObjectContext deleteObject:myElement]; then I can use my elements: myElement.property1 = @"Hello"; This works pretty well even though I think this is probably not the most optimal way to do it... Then I try to use it in my UITableView... the problem is that the object get released after the initialization. My table becomes empty when I move it! Thanks edit: I've also tried to copy the element ([myElement copy]) but I get an error...

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  • ruby on rails has_many through relationship

    - by BennyB
    Hi i'm having a little trouble with a has_many through relationship for my app and was hoping to find some help. So i've got Users & Lectures. Lectures are created by one user but then other users can then "join" the Lectures that have been created. Users have their own profile feed of the Lectures they have created & also have a feed of Lectures friends have created. This question however is not about creating a lecture but rather "Joining" a lecture that has been created already. I've created a "lecturerelationships" model & controller to handle this relationship between Lectures & the Users who have Joined (which i call "actives"). Users also then MUST "Exit" the Lecture (either by clicking "Exit" or navigating to one of the header navigation links). I'm grateful if anyone can work through some of this with me... I've got: Users.rb model Lectures.rb model Users_controller Lectures_controller then the following model lecturerelationship.rb class lecturerelationship < ActiveRecord::Base attr_accessible :active_id, :joinedlecture_id belongs_to :active, :class_name => "User" belongs_to :joinedlecture, :class_name => "Lecture" validates :active_id, :presence => true validates :joinedlecture_id, :presence => true end lecturerelationships_controller.rb class LecturerelationshipsController < ApplicationController before_filter :signed_in_user def create @lecture = Lecture.find(params[:lecturerelationship][:joinedlecture_id]) current_user.join!(@lecture) redirect_to @lecture end def destroy @lecture = Lecturerelationship.find(params[:id]).joinedlecture current_user.exit!(@user) redirect_to @user end end Lectures that have been created (by friends) show up on a users feed in the following file _activity_item.html.erb <li id="<%= activity_item.id %>"> <%= link_to gravatar_for(activity_item.user, :size => 200), activity_item.user %><br clear="all"> <%= render :partial => 'shared/join', :locals => {:activity_item => activity_item} %> <span class="title"><%= link_to activity_item.title, lecture_url(activity_item) %></span><br clear="all"> <span class="user"> Joined by <%= link_to activity_item.user.name, activity_item.user %> </span><br clear="all"> <span class="timestamp"> <%= time_ago_in_words(activity_item.created_at) %> ago. </span> <% if current_user?(activity_item.user) %> <%= link_to "delete", activity_item, :method => :delete, :confirm => "Are you sure?", :title => activity_item.content %> <% end %> </li> Then you see I link to the the 'shared/join' partial above which can be seen in the file below _join.html.erb <%= form_for(current_user.lecturerelationships.build(:joinedlecture_id => activity_item.id)) do |f| %> <div> <%= f.hidden_field :joinedlecture_id %> </div> <%= f.submit "Join", :class => "btn btn-large btn-info" %> <% end %> Some more files that might be needed: config/routes.rb SampleApp::Application.routes.draw do resources :users do member do get :following, :followers, :joined_lectures end end resources :sessions, :only => [:new, :create, :destroy] resources :lectures, :only => [:create, :destroy, :show] resources :relationships, :only => [:create, :destroy] #for users following each other resources :lecturerelationships, :only => [:create, :destroy] #users joining existing lectures So what happens is the lecture comes in my activity_feed with a Join button option at the bottom...which should create a lecturerelationship of an "active" & "joinedlecture" (which obviously are supposed to be coming from the user & lecture classes. But the error i get when i click the join button is as follows: ActiveRecord::StatementInvalid in LecturerelationshipsController#create SQLite3::ConstraintException: constraint failed: INSERT INTO "lecturerelationships" ("active_id", "created_at", "joinedlecture_id", "updated_at") VALUES (?, ?, ?, ?) Also i've included my user model (seems the error is referring to it) user.rb class User < ActiveRecord::Base attr_accessible :email, :name, :password, :password_confirmation has_secure_password has_many :lectures, :dependent => :destroy has_many :lecturerelationships, :foreign_key => "active_id", :dependent => :destroy has_many :joined_lectures, :through => :lecturerelationships, :source => :joinedlecture before_save { |user| user.email = email.downcase } before_save :create_remember_token validates :name, :presence => true, :length => { :maximum => 50 } VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i validates :email, :presence => true, :format => { :with => VALID_EMAIL_REGEX }, :uniqueness => { :case_sensitive => false } validates :password, :presence => true, :length => { :minimum => 6 } validates :password_confirmation, :presence => true def activity # This feed is for "My Activity" - basically lectures i've started Lecture.where("user_id = ?", id) end def friendactivity Lecture.from_users_followed_by(self) end # lECTURE TO USER (JOINING) RELATIONSHIPS def joined?(selected_lecture) lecturerelationships.find_by_joinedlecture_id(selected_lecture.id) end def join!(selected_lecture) lecturerelationships.create!(:joinedlecture_id => selected_lecture.id) end def exit!(selected_lecture) lecturerelationships.find_by_joinedlecture_id(selected_lecture.id).destroy end end Thanks for any and all help - i'll be on here for a while so as mentioned i'd GREATLY appreciate someone who may have the time to work through my issues with me...

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  • android SQLite vs Flat Files

    - by mixm
    hi. im creating a game right now and im a bit stuck on how to implement storage of levels. i need to be able to download level files from the internet ota. im not so familiar with transferring files ota, but i have some experience with databases (mysql). what would be a better way of storing the game's level data?

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  • Decimal rounding strategies in enterprise applications

    - by Sapphire
    Well, I am wondering about a thing with rounding decimals, and storing them in DB. Problem is like this: Let's say we have a customer and a invoice. The invoice has total price of $100.495 (due to some discount percentage which is not integer number), but it is shown as $100.50 (when rounded, just for print on invoice). It is stored in the DB with the price of $100.495, which means that when customer makes a deposit of $100.50 it will have $0.005 extra on the account. If this is rounded, it will appear as $0, but after couple of invoices it would keep accumulating, which would appear wrong (although it actually is not). What is best to do in this case. Store the value of $100.50, or leave everything as-is?

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  • filter duplicates in SQL join

    - by Will
    When using a SQL join, is it possible to keep only rows that have a single row for the left table? For example: select * from A, B where A.id = B.a_id; a1 b1 a2 b1 a2 b2 In this case, I want to remove all except the first row, where a single row from A matched exactly 1 row from B. I'm using MySQL.

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  • many-to-many-to-many, incl alignment of data from diff sources

    - by JefeCoon
    Re-factoring dbase to support many:many:many. At the second and third levels we need to preserve end-user 'mapping' or aligning of data from different sources, e.g. Order 17 FirstpartyOrderID => aha LineItem_for_BigShinyThingy => AA-1 # maps to 77-a LineItem_for_BigShinyThingy => AA-2 # maps to 77-b, 77-c LineItem_for_LittleWidget => AA-x # maps to 77-zulu, 77-alpha, 99-foxtrot LineItem_for_LittleWidget => AA-y # maps to 77-zulu, 99-foxtrot LineItem_for_LittleWidget => AA-z # maps to 77-alpha ThirdpartyOrderID => foo LineItem_for_BigShinyThingy => 77-a LineItem_for_BigShinyThingy => 77-b LineItem_for_BigShinyThingy => 77-c LineItem_for_LittleWidget => 77-zulu LineItem_for_LittleWidget => 77-alpha ThirdpartyOrderID => bar LineItem_for_LittleWidget => 99-foxtrot Each LineItem has daily datapoints reported from its own source (Firstparty|Thirdparty). In our UI & app we provide tools to align these, then we'd like to save them into the cleanest possible schema for querying, enabling us to diff the reported daily datapoints, and perform other daily calculations (which we'll store in the dbase also, fortunately that should be cake once we've nailed this). We need to map related [firstparty|thirdparty]line_items which have their own respective datapoints. We'll be using the association to pull each line_items collection of datapoints for summary and discrepancy calculations. I'm considering two options, std has_many,through x2 --or-- possibly (scary) ubermasterjoin table OptionA: order<<-->> order_join_table[id,order_id,firstparty_order_id,thirdparty_order_id] <<-->>line_item order_join_table[firstparty_order_id]-->raw_order[id] order_join_table[thirdparty_order_id]-->raw_order[id] raw_order-->raw_line_items[raw_order_id] line_item<<-->> line_item_join[id,LI_join_id,firstparty_LI,thirdparty_LI <<-->>raw_line_items line_item_join[firstparty_LI]-->raw_line_item[id] line_item_join[thirdparty_LI]-->raw_line_item[id] raw_line_item<<-->>datapoints = we rely upon join to store all mappings of first|third orders & line_items = keys to raw_* enable lookup of these order & line_item details = concerns about circular references and/or lack of correct mapping logic, e.g order--line_item--raw_line_items vs. order--raw_order--raw_line_items OptionB: order<<-->> join_master[id,order_id,FP_order_id,TP_order_id,FP_line_item_id,TP_line_item_id] join_master[FP_order_id & TP_order_id]-->raw_order[id] join_master[FP_line_item_id & TP_line_item_id]-->raw_line_item[id] = every combo of FP_line_item + TP_line_item writes a record into the join_master table = "theoretically" queries easy/fast/flexible/sexy At long last, my questions: a) any learnings from painful firsthand experience about how best to implement/tune/optimize many-to-many-to-many relationships b) in rails? c) any painful gotchas (circular references, slow queries, spaghetti-monsters) to watch out for? d) any joy & goodness in Rails3 that makes this magically easy & joyful? e) anyone written the "how to do many-to-many-to-many schema in Rails and make it fast & sexy?" tutorial that I somehow haven't found? If not, I'll follow up with our learnings in the hope it's helpful.. Thanks in advance- --Jeff

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  • why does cx_oracle execute() not like my string now?

    - by Frank Stallone
    I've downloaded cx_oracle some time ago and wrote a script to convert data to XML. I've had to reisntall my OS and grabbed the latest version of cx_Oracle (5.0.3) and all of the sudden my code is broken. The first thing was that cx_Oracle.connect wanted unicode rather string for the username and password, that was very easy to fix. But now it keeps failing on the cursor.execute and tells me my string is not a string even when type() tells me it is a string. Here is a test script I initally used ages ago and worked fine on my old version but does not work on cx_Oracle now. import cx_Oracle ip = 'url.to.oracle' port = 1521 SID = 'mysid' dsn_tns = cx_Oracle.makedsn(ip, port, SID) connection = cx_Oracle.connect(u'name', u'pass', dsn_tns) cursor = connection.cursor() cursor.arraysize = 50 sql = "select isbn, title_code from core_isbn where rownum<=20" print type(sql) cursor.execute(sql) for isbn, title_code in cursor.fetchall(): print "Values from DB:", isbn, title_code cursor.close() connection.close() When I run that I get: Traceback (most recent call last): File "C:\NetBeansProjects\Python\src\db_temp.py", line 48, in cursor.execute(sql) TypeError: expecting None or a string Does anyone know what I may be doing wrong?

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  • Designing a table to store EXIF data

    - by rafale
    I'm looking to get the best performance out of querying a table containing EXIF data. The queries in question will only search the EXIF data for the specified strings and return the row index on a match. With that said, would it better to store the EXIF data in a table with separate columns for each of the tags, or would storing all of the tags in a single column as one long delimited string suit me just as well? There are around 115 EXIF tags I'll be storing, and each record would be around 1500 to 2000 chars in length if concatenated into a single string.

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  • How to select product that have the maximum price of each category?

    - by kimleng
    The below is my table that has the item such as: ProductId ProductName Category Price 1 Tiger Beer $12.00 2 ABC Beer $13.99 3 Anchor Beer $9.00 4 Apolo Wine $10.88 5 Randonal Wine $18.90 6 Wisky Wine $30.19 7 Coca Beverage $2.00 8 Sting Beverage $5.00 9 Spy Beverage $4.00 10 Angkor Beer $12.88 And I suppose that I have only three category in this table (I can have a lot of category in this table). And I want to show the maximum product's price of each category in this table.

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  • C# Find out what column caused the Sql Exception

    - by PaN1C_Showt1Me
    Hi. I'm getting an exception from SQL Data Reader (MS SQL as datastore) and I'd like to know which column name causes this Exception to be thrown. But I cannot find it in the InnerException.. nowhere. ((System.InvalidOperationException)ex.InnerException).StackTrace: System.Data.SqlClient.SqlDataReader.ReadColumnHeader(Int32 i) System.Data.SqlClient.SqlDataReader.IsDBNull(Int32 i) ... Where is it hidden please ?

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  • how to join 3 relational tables

    - by orioncabbar
    Hello there, how to join 3 relational tables with the structure: t1 | id t2 | id | rating t3 | source_id | relation t3 stores the data of a field which t1 and t2 uses both. so source_id field can be t1's id or t2's id. input : t1 id output : t2 rating an example: **t1** id | --------- 42 | **t2** id | rating ------------- 37 | 9.2 **t3** id | source_id -------------- 42 | 1 37 | 1 26 | 2 23 | 1 what i want is to get 9.2 output with 42 input. can you do that in one sql query?

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  • Better data-structure design

    - by Tempname
    Currently in my application I have a single table that is giving me a bit of trouble. The issue at hand is I have a value object that is mapped to this table. When the data is returned to me as an array of value objects, I have to then loop through this array and begin my recursion by matching the ParentID to parent ObjectID's. The column ParentID is either null (acts a parent) or it holds the value of an ObjectID. I know there has to be a better way to create this data structure so that I do not have to do recursive loops to match ParentID's with their ObjectID's. Any help with this is greatly appreciated. Here is the table in describe form: +----------------+------------------+------+-----+---------------------+-----------------------------+ | Field | Type | Null | Key | Default | Extra | +----------------+------------------+------+-----+---------------------+-----------------------------+ | ObjectID | int(11) unsigned | NO | PRI | NULL | auto_increment | | ObjectHeight | decimal(6,2) | NO | | NULL | | | ObjectWidth | decimal(6,2) | NO | | NULL | | | ObjectX | decimal(6,2) | NO | | NULL | | | ObjectY | decimal(6,2) | NO | | NULL | | | ObjectLabel | varchar(255) | NO | | NULL | | | TemplateID | int(11) unsigned | NO | MUL | NULL | | | ObjectTypeID | int(11) unsigned | NO | MUL | NULL | | | ParentID | int(11) unsigned | YES | MUL | NULL | | | CreationDate | datetime | YES | | 0000-00-00 00:00:00 | | | LastModifyDate | timestamp | YES | | NULL | on update CURRENT_TIMESTAMP | +----------------+------------------+------+-----+---------------------+-----------------------------+e

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  • sqlite3 date operations when joining two tables in a view?

    - by duncan
    In short, how to add minutes to a datetime from an integer located in another table, in one select statement, by joining them? I have a table P(int id, ..., int minutes) and a table S(int id, int p_id, datetime start) I want to generate a view that gives me PS(S.id, P.id, S.start + P.minutes) by joining S.p_id=P.id The problem is, if I was generating the query from the application, I can do stuff like: select datetime('2010-04-21 14:00', '+20 minutes'); 2010-04-21 14:20:00 By creating the string '+20 minutes' in the application and then passing it to sqlite. However I can't find a way to create this string in the select itself: select p.*,datetime(s.start_at, formatstring('+%s minutes', p.minutes)) from p,s where s.p_id=p.id; Because sqlite as far the documentation tells, does not provide any string format function, nor can I see any alternative way of expressing the date modifiers.

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  • Django: How/Where to store a value for a session without unnecessary DB hits

    - by GerardJP
    Hi all, I have an extended userprofile with AUTH_PROFILE_MODULE (ref: http://tinyurl.com/yhracqq) I would like to set a user.is_guru() method similar to user.is_active(). This would results for al views (or rather templates) to e.g. disable/enable certain user messages, displaying of widgets, etc. The boolean is stored in the extended user profile model, but I want to avoid hitting the DB for every view. So the questions is .. Do I use a context_processor, a template tag, session_dict or what have you to, possible cached, store this info for the duration of the users visit. Note: I dont have performance issues, so it's definitely filed under premature optimization. I just want to avoid generating extra work in the future :). Any pointers are very welcome. Thanx and greetz! Gerard.

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  • "select * into table" Will it work for inserting data into existing table

    - by Shantanu Gupta
    I am trying to insert data from one of my existing table into another existing table. Is it possible to insert data into any existing table using select * into query. I think it can be done using union but in that case i need to record all data of my existing table into temporary table, then drop that table and finally than apply union to insert all records into same table eg. select * into #tblExisting from tblExisting drop table tblExisting select * into tblExisting from #tblExisting union tblActualData Here tblExisting is the table where I actually want to store all data tblActualData is the table from where data is to be appended to tblExisting. Is it right method. Do we have some other alternative ?

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  • MySql - set of time stamped data (timestamp,event) calculating events per day

    - by Kevin Ohashi
    I have a table: id, datetime, event i also have table dates: date (Y-m-d format) the problem is some days don't have any events, I would like them to show 0 (or null) SELECT DATE_FORMAT(table.timestamp, '%Y-%m-%d') ydm, count(table.fkUID) FROM `table` where table.fkUID=$var group by ydm; is there some way to join or use conditional statements to make the result show: date|count ---------- 2010-05-23| 5 2010-05-24| 0 <--- this line just doesn't exist in my query. 2010-05-26| 3

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  • Question about OOP and objects.

    - by loddn
    I have a school assignment, a Dog Show. My assignment is to create a website where vistors can display results and Judges and Secretary can admin, crud. I have a small problem one part of the assignment. The result should be based on two protokols from different judges and after that checked by the secretary before the result is displayed for the user. I have to say i'm fairly new to programming and so i need some smart suggestions on how to design and implement this. The assignment should cover both a db and c# (.net mvc). Q1: How do i create a object (result)that depends on two other objects(protocol)? Is that even needed? Q2: How to solve this in a relational db?

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