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  • Question about mysql indexes on low to medium cardinality columns

    - by Kevin J
    I have a general question about the way that database indexing works, particularly in mysql. Let's say I have a table with a million rows with a column "ClientID" that is distributed relatively equally among 30 values. Thus, this column is very low cardinality (30) relative to the primary key (1 million). Now, I understand that you shouldn't create indexes on low cardinality fields. However, in this case, queries are only ever done with one of the 30 clientIDs. Thus, wouldn't creating an index on ClientID be helpful, as the search space is automatically reduced to 1/30th what it normally would be? Or is my understanding of how the index works flawed? Thanks

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  • Ruby on Rails and database associations

    - by Marco
    Hi to all, I'm new to the Ruby world, and there is something unclear to me in defining associations between models. The question is: where is the association saved? For example, if i create a Customer model by executing: generate model Customer name:string age:integer and then i create an Order model generate model Order description:text quantity:integer and then i set the association in the following way: class Customer < ActiveRecord::Base has_many :orders end class Order < ActiveRecord::Base belongs_to :customer end I think here is missing something, for example the foreign key between the two entities. How does it handle the associations created with the keywords "has_many" and "belongs_to" ? Thanks

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  • PHP - Select from database the same query

    - by How to PHP
    I created a table that contains the name of the user and his job, and created PHP page that shows me all the users that works doctor, I entered doctor into a variable then I selected from the table where Jobs equal to $doctor, that is great, but I need it to get the same Jobs into a table in the page and the other same jobs into a table in the same page. this is my code that shows only the users works doctor in one table, <html> <h1>Doctors</h1> </html> <?php mysql_connect('localhost','root',''); mysql_select_db('data'); $doctor='doctor'; $query= mysql_query("SELECT * FROM `users` WHERE `job` = '$doctor'")or die(mysql_error()); while ($arr = mysql_fetch_array($query)) $name= $arr['name']; echo $name; } ?> That shows me doctors when I put doctor in a variable I want to show all same Jobs in a table. Is there is a way to do this? Thanks :)

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  • Host...not allowed error in ODBC connection, while connecting to an online MySQL database

    - by sqlchild
    I have downloaded MySQL ODBC Connector 5.1. Now am trying to setup the DSN. But am getting the error: Connection Failed : [HY000] [MySQL] [ODBC 5.1 Driver]Host '117.x.x.x' is not allowed to connect to this MySQL server My server url is server.myweb.com - this name am entering in the TCP/IP Server and Port =3306. I have also entered the userid and password , which is the one which i enter when i open www.myweb.com/cpanel Is this a version problem? Should the version of MySQL on my server also be 5.1, i.e. the one of the ODBC? Please help.

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  • Database Table design for Weekdays and Values

    - by Ved
    Guys, I would love to here your ideas on this. I am creating a table which will store weekly shift hours for employees. for example: Jon works 9:00am tp 9:00pm Monday , 10:00 AM to 5:00PM on Tuseday etc.... How should i go on designing this table. I thought of 2 options. (1) For every record I can have two lines for AM and PM and have columns for Monday to Sunday ID | ParentID | Type | Monday | Tuseday ......Sunday 1 | 1 | AM | 9:00 | 9:00 12:00 2 | 1 | PM | 9:00 | 5:00 02:00 3 | 2 | AM | 10:00 | 4 | 2 | PM | 10:00 | (2) I can save Preference in XML format in one column ID | Info 1 | |Hours|Monday|9:00 AM - 9:00PM|Monday|Tuseday........|Hours Any better ideas ? Thanks

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  • jQuery : how to manipulate indexes?

    - by Gabriel Theron
    Should not be such a hard question... I'm just having a hard time figuring out how to make operations on some jquery elements, particularly their indexes. Teh codez: $( "#docSlider" ).css("background-image", "url(../../bundles/mypath/images/maquette/img" + $( "#selectable li" ).index( this ) + (".jpg)")); I want to make the name of the picture I load depend on the index of a jQuery selectable. So I grab the index and try to add 1... but it can't work because "+" is also a concatenator. I've tried to parseInt as well, but it was always worth 0. How do I simply transform the index to an integer and then concatenate it with the rest of the string? Thank you in advance! Edit : I'm using a function that already exists, so I can hardly change the parameters (well, I guess I can't...)

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  • php database session handling problem in IE8!

    - by psyb0rg
    I've got an html page from where Im making this call periodically: function logon(id) { $.get("data.php", { action: 'online', userID: id}, function(data){ $("#msg").html(data); }); } What this does is it calls this SQL script in data.php: $sql = "update user_sessions set expires=(expires + 2) where userID = $userID"; mysql_query($sql, $conn) or die(mysql_error()); echo $sql; I can see by the echo that the sql syntax and values are correct, but THE CHANGES TO THE expires FIELD ARE NOT DONE, ONLY IN IE8!! It works fine in other ff, safari, chrome, ie6 and 7. There is nothing browser specific about making this sql call, but the user_sessions table is used to store PHP's sessions. Im only increasing the session expiry time when the call is made. What in IE8's session handling is preventing the session time from changing? Is there any caching or cookie problem that needs to be changed?

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  • MySQL Database Design with Internationalization

    - by Some name
    Hello, I'm going to start work on a medium sized application, and i'm planning it's db design. One thing that I'm not sure about is this. I will have many tables which will need internationalization, such as: "membership_options, gender_options, language_options etc" Each of these tables will share common i18n fields, like: "title, alternative_title, short_description, description" In your opinion which is the best way to do it? Have an i18n table with the same fields for each of the tables that will need them? or do something like: Membership table Gender table ---------------- -------------- id | created_at id | created_at 1 - 22.03.2001 1 - 14.08.2002 2 - 22.03.2001 2 - 14.08.2002 General translation table ------------------------- record_id | table_name | string_name | alternative_title| .... |id_language 1 - membership regular null 1 (english) 1 - membership normale null 2 (italian) 1 - gender man null 1(english) 1 -gender uomo null 2(italian) This would avoid me repeating something like: membership_translation table ----------------------------- membership_id | name | alternative_title | id_lang 1 regular null 1 1 normale null 2 gender_translation table ----------------------------- gender_id | name | alternative_title | id_lang 1 man null 1 1 uomo null 2 and so on, so i would probably reduce the number of db tables, but i'm not sure about performance.I'm not much of a DB designer, so please let me know.

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  • Database schema for a library

    - by ABach
    Hi all - I'm designing a library management system for a department at my university and I wanted to enlist your eyes on my proposed schema. This post is primarily concerned with how we store multiple copies of each book; something about what I've designed rubs me the wrong way, and I'm hoping you all can point out better ways to tackle things. For dealing with users checking out books, I've devised three tables: book, customer, and book_copy. The relationships between these tables are as follows: Every book has many book_copies (to avoid duplicating the book's information while storing the fact that we have multiple copies of that book). Every user has many book_copies (the other end of the relationship) The tables themselves are designed like this: ------------------------------------------------ book ------------------------------------------------ + id + title + author + isbn + etc. ------------------------------------------------ ------------------------------------------------ customer ------------------------------------------------ + id + first_name + first_name + email + address + city + state + zip + etc. ------------------------------------------------ ------------------------------------------------ book_copy ------------------------------------------------ + id + book_id (FK to book) + customer_id (FK to customer) + checked_out + due_date + etc. ------------------------------------------------ Something about this seems incorrect (or at least inefficient to me) - the perfectionist in me feels like I'm not normalizing this data correctly. What say ye? Is there a better, more effective way to design this schema? Thanks!

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  • c# reading integer fields from database

    - by arnoldino
    what is wrong with this code? try { if (cmd == null) getConnection(); cmd.CommandText = "Select id from HMonthInventary where machine_id=37"; SQLiteDataReader reader = cmd.ExecuteReader(); if (reader.HasRows==true) { reader.Read(); string s = reader[0].ToString(); // return first element reader.Close(); return s; } reader.Close(); return null; } catch (Exception e) { MessageBox.Show("Caught exception: " + e.Message+"|"+cmd.CommandText); return null; } I checked the sql statement, it turns the right value. why can't I read it? the returnvalue is "".

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  • design an extendable database model

    - by wishi_
    Hi! Currently I'm doing a project whose specifications are unclear - well who doesn't. I wonder what's the best development strategy to design a DB, that's going to be extended sooner or later with additional tables and relations. I want to include "changeability". My main concern is that I want to apply design patterns (it's a university project) and I want to separate the constant factors from those, that change by choosing appropriate design patterns - in my case MVC and a set of sub-patterns at model level. When it comes to the DB however, I may have to resdesign my model in my MVC approach, because my domain model at a later stage my require a different set of classes representing the DB tables. I use Hibernate as an abstraction layer between DB and application. Would you start with a very minimal DB, just a few tables and relations? And what if I want an efficient DB, too? I wonder what strategies are applied in the real world. Stakeholder analysis for example isn't a sufficient planing solution when it comes to changing requirements. I think - at a DB level - my design pattern ends. So there's breach whose impact I'd like to minimize with a smart strategy.

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  • Database Design for One to One relationships

    - by Greelmo
    I'm trying to finalize my design of the data model for my project, and am having difficulty figuring out which way to go with it. I have a table of users, and an undetermined number of attributes that apply to that user. The attributes are in almost every case optional, so null values are allowed. Each of these attributes are one to one for the user. Should I put them on the same table, and keep adding columns when attributes are added (making the user table quite wide), or should I put each attribute on a separate table with a foreign key to the user table. I have decided against using the EAV model. Thanks!

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  • Using a singleton database class in functions and multiple scripts(PHP) - best use methods

    - by dscher
    I have a singleton db connection which I get with: $dbConnect = myDatabase::getInstance(); which is easy enough. My question is what is the least rhetorical and legitimate way of using this connection in functions and classes? It seems silly to have to declare the variable global, pass it into every single function, and/or recreate this variable within every function. Is there another answer for this? Obviously I'm a noob and I can work my way around this problem 10 different ways, none of which is really attractive to me. It would be a lot easier if I could have that $dbConnect variable accessible in any function without needing to declare it global or pass it in. I do know I can add the variable to the $_SERVER array...is there something wrong with doing this? It seems somewhat inappropriate to me. Another quick question: Is it bad practice to do this: $result = myDatabase::getInstance()-query($query); from directly within a function?

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  • Advantage Database Server: in-memory queries.

    - by ie
    As far as I know, ADS v.10 tries to keep result of query in memory until it is a quite huge. The same should be true for the __output table and for temporary tables. When the result becoming large, swapping stated. The question is what memory limit is set for a query, a worker, whatever? Could this limit be configured? Thanks.

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  • Is there a flat-file database that is supported by Silverlight?

    - by Anton Kanevsky
    I am looking for a flat-file (or serverless) database that I can connect to a C# Silverlight application. There has to be one, but I can't find anything. EDIT: SQLite is an example of a flat-file database. A flat-file database in my view is any database that does not require a server. Unfortunately, SQLite does not work with Silverlight. What I want to achieve is to be able to store, update and delete entries from the database. In my application, there is a chart with sectors and nodes. I want to be able to edit sectors and store their settings in the database, and I want to be able to add/retrieve/edit/delete nodes on the chart. The database needs to be free for educational purposes. Thanks.

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  • How to Implement Web Based Find File Database Text Search

    - by neversaint
    I have series of files like this: foo1.txt.gz foo2.txt.gz bar1.txt.gz ..etc.. and a tabular format files that describe the file foo1 - Explain foo1 foo2 - Explain foo2 bar1 - Explain bar1 ..etc.. What I want to do is to have a website with a simple search bar and allow people to type foo1 or just foo and finally return the gzipped file(s) and the explanation of the file(s). What's the best way to implement this. Sorry I am totally new in this area.

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  • How to Implement Web Based Find File Database Via Text Search

    - by neversaint
    I have series of files like this: foo1.txt.gz foo2.txt.gz bar1.txt.gz ..etc.. and a tabular format file that describe those files: foo1 - Explain foo1 foo2 - Explain foo2 bar1 - Explain bar1 ..etc.. What I want to do is to have a website with a simple search bar and allow people to type foo1 or just foo and finally return the gzipped file(s) and the related explanation of the file(s). What's the best way to implement this and what kind of tools should I use. Sorry I am totally new in this area.

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  • Help needed in database design for application of Timetable Generation

    - by Himadri
    I am planning for an application of time-table generation. I wanted the data such as standardname, teachername, standard wise subjects and also relate the corresponding teacher with the subject and standard. I had think like, StandardMaster(stdid,stdname) TeacherMaster(teacherid,teachername) SubjectMaster(subid,subname,stdid) What more I need? Any corrections needed in these three tables?

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  • Fulltext and composite indexes and how they affect the query

    - by Brett
    Just say I had a query as below.. SELECT name,category,address,city,state FROM table WHERE MATCH(name,subcategory,category,tag1) AGAINST('education') AND city='Oakland' AND state='CA' LIMIT 0, 10; ..and I had a fulltext index as name,subcategory,category,tag1 and a composite index as city,state; is this good enough for this query? Just wondering if something extra is needed when mixing additional AND's when making use of the fulltext index with the MATCH/AGAINST. Edit: What I am trying to understand is, what happens with the additional columns that are within the query but are not indexed in the chosen index (the fulltext index), the above example being city and state. How does MySQL now find the matching rows for these since it can't use two indexes (or can it?) - so, basically, I'm trying to understand how MySQL goes about finding the data optimally for the columns NOT in the chosen fulltext index and if there is anything I can or should do to optimize the query.

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