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• A B+tree simple implementation in C

  - by initpy

  Hi guys, I'm working on a fun project where I need a simple key/value store that uses B+Trees. I studied them some years ago, and to be honest, I don't want to reinvent the wheel, so I'm looking for a simple implementation in C of b+tree that I can just include in my project. I know of sqlite's, dbm's and tokyocabinet's ones but they're a little too "complicated" for my needs. Is there any (even pedagogical) work on this you can refer me to? Do you have some code to share? Thanks a lot!

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• Syntax Error with MySQL 5.1 Server

  - by Mr.Z

  I am trying to connect to a server remotely using the command line client window. I am using MySQL 5.1 and I do not know why I am getting syntax error. If you can help me, that would be much appreciated. username as user password as pass hostname as example.com I have tried: mysql> -u user -h example.com -p ; mysql> -h example.com -u user -p ; I have looked at the reference manual and other verisons of remote connection with Server 5.1 but I can't see the syntax error.

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• Oracle (Old?) Joins - A tool/script for conversion?

  - by Grasper

  I have been porting oracle selects, and I have been running across a lot of queries like so: SELECT e.last_name, d.department_name FROM employees e, departments d WHERE e.department_id(+) = d.department_id; ...and: SELECT last_name, d.department_id FROM employees e, departments d WHERE e.department_id = d.department_id(+); Are there any guides/tutorials for converting all of the variants of the (+) syntax? What is that syntax even called (so I can scour google)? Even better.. Is there a tool/script that will do this conversion for me (Preferred Free)? An optimizer of some sort? I have around 500 of these queries to port.. When was this standard phased out? Any info is appreciated.

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• The Biggest Data Management problems

  - by Ben Breen

  Where does current technology fall short of industry demands in the context of data and information management? In other words, where should the software engineering industry as a whole be focusing its efforts in these areas?

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• Can I create a table with check constrain whose values are dependent on sql query

  - by Shantanu Gupta

  Is it possible to create a table which has a check constraint on one of the column whose value lies within the result set given by another sql query eg. create table tablename ( name varchar(10), rollno int )check rollno in (select rollno from anotherDatabase.TableName,candidateRoll) or any thing like that. I dont have to use it anywhere but still want to know.

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• django related_name for field clashes.

  - by Absolute0

  I am getting a field clash in my models: class Visit(models.Model): user = models.ForeignKey(User) visitor = models.ForeignKey(User) Error: One or more models did not validate: profiles.visit: Accessor for field 'user' clashes with related field 'User.visit_set'. Add a related_name argument to the definition for 'user'. profiles.visit: Accessor for field 'visitor' clashes with related field 'User.visit_set'. Add a related_name argument to the definition for 'visitor'. what would be a sensible 'related_field' to use on visitor field? This model basically represents the visits that take place to a particular user's profile. Also should I replace any of the ForeignKey's with a ManyToManyField? The logic is a bit confusing. Edit: This seems to fix it, but I am unsure if its what I want. :) class Visit(models.Model): user = models.ForeignKey(User) visitor = models.ForeignKey(User, related_name='visitors')

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• Non-normalized association with legacy tables in Rails and ActiveRecord

  - by Thomas Holmström

  I am building a Rails application accessing a legacy system. The data model contains Customers which can have one or more Subscriptions. A Subscription always belong to one and only one Customer. Though not needed, this association is represented through a join table "subscribes", which do not have an id column: Column | Type | Modifiers -----------------+---------+----------- customer_id | integer | not null subscription_id | integer | not null I have this coded as a has_and_belongs_to_many declarations in both Customer and Subscription class Customer < Activerecord::Base has_and_belongs_to_many :subscriptions, :join_table => "subscribes", :foreign_key => "customer_id", :association_foreign_key => "subscription_id" end class Subscription < Activerecord::Base has_and_belongs_to_many :customers, :join_table => "subscribes", :foreign_key => "subscription_id", :association_foreign_key => "customer_id" end The problem I have is that there can only ever be one customer for each subscription, not many, and the join table will always contain at most one row with a certain customer_id. And thus, I don't want the association "customers" on a Subscription which returns an array of (at most one) Customer, I really do want the relation "customer" which returns the Customer associated. Is there any way to force ActiveRecord to make this a 1-to-N relation even though the join table itself seems to make it an N-to-M relation? --Thomas

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• why is there extra using where in execution plan of query

  - by user366534

  I see plan of query: EXPLAIN SELECT * FROM `subscribers` WHERE state =4 AND date_added < '2010-12-23 11:47:45' It shows: id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE subscribers range state_date_added state_date_added 9 NULL 8 Using where Here is indexes of table: Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment subscribers 0 PRIMARY 1 subscriber_id A 382039 NULL NULL BTREE subscribers 0 email_list_id 1 email_address A 191019 NULL NULL BTREE subscribers 0 email_list_id 2 list_id A 382039 NULL NULL BTREE subscribers 1 FK_list_id 1 list_id A 10 NULL NULL BTREE subscribers 1 state_date_added 1 state A 12 NULL NULL BTREE subscribers 1 state_date_added 2 date_added A 8128 NULL NULL BTREE The last two lines describes index what is supposed for the query. Why is there in extra column using where? Even If I fetch only state and date_added column, it has in extra column: Using where; Using index. I understand why it has using index, but I don't understand Using where here.

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• SQLServer using too much memory

  - by Israel Pereira Valverde

  I have installed on my desktop machine (with windows 7) SQLServer 2008 R2 Express. I have only one local server running (./SQLEXPRESS) but the sqlserver process is taking ALL the RAM possible. With an machine with 3GB of RAM the things starts to get slow, so I limited the maximun amount of RAM in the server, and now, constantly the SQLServer give some error messages that the memory is not enought. It's using 1GB of RAM with only one LOCAL server with 2 databases completely empty, how 1GB of RAM isn't enought ? When the process start it's using an really acceptable amount of memory (around 80MB) but it's keep increasing until it reaches the maximun defined and start to complain about having not enought memory available. In that point I have to restart the server to use it again. I have read about an hotfix to solve one of the errors I got from sqlserver: There is insufficient system memory in resource pool 'internal' to run this query But it's already installed on my sqlserver. Why it's using so much memory?

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• Normalise this Table?

  - by Abs

  Hello all, I am creating a social bookmarking app. I am having a re-thought of the DB design in the middle of development. Should I normalise the bookmarks table and remove the tag columns that I have into a separate table. I have 10 tags per bookmark and therefore 10 columns per record (per bookmark). It seems to me that breaking the table into two would just mean I would have to do a join but the way I currently have it, its a straight select - but the table doesn't feel right...? Thanks all

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• Django: Serializing models in a nested data structure?

  - by Rosarch

  It's easy to serialize models in an iterable: def _toJSON(models): return serializers.serialize("json", models, ensure_ascii=False) What about when I have something more complicated: [ (Model_A_1, [Model_B_1, Model_B_2, Model_B_3]), (Model_A_2, [Model_B_3, Model_B_4, Model_B_5, Model_B_59]), (Model_A_3, [Model_B_6, Model_B_7]), ] I tried serializing each model as it was added to the structure, then serializing the whole thing with simplejson.dumps, but that causes the JSON defining each model to be escaped. Is there a better way to do this?

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• Convert MSAccess Project Management Application to PHP/MySQL: Which Methodology?

  - by zzapper

  I've got to convert a not terribly complicated bespoke project management system from MsAccess Application to PHP/MySQL. I've been programming for donkey's years but embarrassingly know practically nothing about modern methodologies. So the old 'learning curve' versus 'improved efficiency' conundrum rears its ugly head once again. Although I've Googled up some stuff I don't want to prejudice your suggestions, where would you start, I'm at your mercy?

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• Select where and where not

  - by Simon

  I have a table containing lessons that I called "cours" (french) and I have several cours inside and I have linked them to students with a table between them to see if they go to the lessons or not. I would like to return data with the SELECT and the data that are NOT select. So, If one student follow 3 courses of 5, I would like to return the 3 courses that he follow and the 2 courses that he doesn't follow. Is there a way to do it ?

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• Python: mysqldb install error

  - by Grenko

  So i've been pulling my hair out trying to install the mysqldb package. When i run the build i get a long transcript of errors, heres just part of it, i would posit it all but its huge list of errors [rv@med240-183 MySQL-python-1.2.3c1]$ sudo python setup.py build [sudo] password for rv: running build running build_py copying MySQLdb/release.py -> build/lib.linux-i686-2.6/MySQLdb running build_ext building '_mysql' extension gcc -pthread -fno-strict-aliasing -DNDEBUG -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i586 -mtune=generic -fasynchronous-unwind-tables -D_GNU_SOURCE -fPIC -fPIC -Dversion_info=(1,2,3,'gamma',1) -D__version__=1.2.3c1 -I/usr/include/mysql -I/usr/include/python2.6 -c _mysql.c -o build/temp.linux-i686-2.6/_mysql.o -g -pipe -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -fasynchronous-unwind-tables -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -fno-strict-aliasing -fwrapv -fPIC -DUNIV_LINUX _mysql.c:36:23: error: my_config.h: No such file or directory _mysql.c:38:19: error: mysql.h: No such file or directory Any ideas?

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• Excel Spreadsheet - Best way to perform an Oracle Query on a cell

  - by Jamie

  Hi there, I have an Excel Spreadsheeet. There is a cell containing a concatenated name and surname (don't ask why), for example: Cell A2 BLOGGSJOE On this cell, I would like to run the following SQL and output it to cell A3, A4 and A5 SELECT i.id, i.forename, i.surname FROM individual i WHERE UPPER(REPLACE('" & A2 & "', ' ', '')) = UPPER(REPLACE(i.surname|| i.forename, ' ', '')) AND NVL(i.ind_efface, 'N') = 'N' Any idea how I could perform an oracle query on each cell and return the result? I have enabled an oracle datasource connection in Excel, just not sure what to do now. Is this a stupid approach, and can you recommend a better more proficient way? Thanks muchly! I lack the necessary experience in this type of thing! :-) EDIT: I am aware that I could just write a simple ruby/php/python/whatever script to loop through the excel spreadsheet (or csv file), and then perform the query etc. but i thought there might be a quick way in excel itself.

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• Creating a Group of Groups in Django

  - by Greg

  I'm creating my own Group model; I'm not referring to the builtin Group model. I want each hroup to be a member of another group (it's parent), but there is the one "top" group that doesn't have a parent group. The admin interface won't let me create a group without entering a parent. I get the error personnel_group.parent_id may not be NULL. My Group model looks like this: class Group(models.Model): name = models.CharField(max_length=50) parent = models.ForeignKey('self', blank=True, null=True) order = models.IntegerField() icon = models.ImageField(upload_to='groups', blank=True, null=True) description = models.TextField(blank=True, null=True) How can I accomplish this? Thanks.

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• what is "=null" and " IS NULL"

  - by user329820

  I want some links for reading about the "=null" and "is null" please help me thanks

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• something about ansi_nulls

  - by user329820

  Hi I have a question that we always say that null =null is false ,I want to know that when the ansi_nulls is off this statement which is "null=null" is also false? thanks

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• ResultSet and aggregation

  - by kachanov

  Ok, I admit my situation is special There is a data system that supports SQL-92 and JDBC interface However the SQL requets are pretty expensive, and in my application I need to retreive the same data multiple times and aggregate it ("group by") on different fields to show different dimensions of the same data. For example on one screen I have three tables that show the same set or records but aggregated by City (1st grid), by Population (2nd grid), by number of babies (3rd grid) This amounts to 3 SQL queries (which is very slow), UNLESS anyone of you can suggest any idea any library from apache commons or from google code, so that I can select all records into ResultSet and get 3 arrays of data group by different fields from this single ResultSet. Am I'm missing some obvious and unexpected solution to this problem?

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• Back out plan for a Web App

  - by nobody

  We need a back out plan for a web app whose first maintenance release is going to production soon. The issue we are facing is even if we back out new EAR and deploy old one , the data which was keyed in using new release would not support old business rules(current), since there is enormous changes in business rules. Can you suggest how do we tackle this issue?

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• MS Access CrossTab query - across 3 tables

  - by Prembo

  Hi, I have the following 3 tables: 1) Sweetness Table FruitIndex CountryIndex Sweetness 1 1 10 1 2 20 1 3 400 2 1 50 2 2 123 2 3 1 3 1 49 3 2 40 3 3 2 2) Fruit Name Table FruitIndex FruitName 1 Apple 2 Orange 3 Peaches 3) Country Name Table CountryIndex CountryName 1 UnitedStates 2 Canada 3 Mexico I'm trying to perform a CrossTab SQL query to end up with: Fruit\Country UnitedStates Canada Mexico Apple 10 20 400 Orange 50 123 1 Peaches 49 40 2 The challenging part is to label the rows/columns with the relevant names from the Name tables. I can use MS Access to design 2 queries, create the joins the fruit/country names table with the Sweetness table perform crosstab query However I'm having trouble doing this in a single query. I've attempted nesting the 1st query's SQL into the 2nd, but it doesn't seem to work. Unfortunately, my solution needs to be be wholly SQL, as it is an embedded SQL query (cannot rely on query designer in MS Access, etc.). Any help greatly appreciated. Prembo.

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• What are the best ways to store Graphs in persistent storage

  - by nicoslepicos

  I am wondering what the best ways to store graphs in persistent storage are, for later analysis, search, clustering, etc. I see neo4j being an option, I am curious if there are also other graph databases available. Does anyone have any insights into how larger social networks store their graph based data (or other sites that require the storage of graph like models, e.g. RDF). What about options like Cassandra, or MySQL?

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• Check value at insert

  - by ThreeFingerMark

  Hello, i have this three tables. Table: Item Columns: ItemID, Title, Content, NoChange (Date) Table: Tag Columns: TagID, Title Table: ItemTag Columns: ItemID, TagID In the Item Table is a Field with NoChange, if this field = true no Tag is allowed to insert a ItemTag value with this ItemID. How can i check this in the insert? For Updates i have this Statement: UPDATE ItemTag SET TagID = ? where ItemID = ? AND TagID = ? AND exists ( select ItemID from Item where ItemID = ? AND NoChange is null)"); Thank you.

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• Creating a Web Service to automatically get information

  - by Sean P

  I want to create some sort of method of creating a web service that will run automatically and run DB queries and some API calls which will then store data that I can use/call without taking the processing or time penalty of doing it every time a user access my web service. Is this possible? If so, point me in the right direction on how to implement something like this Using vb.net and ASP.net Thanks in advance!!

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• Oracle : How can i find the holiday in a business day?

  - by Rajesh Kumar G

  Hi, Consider there are 3 different centers across the country,which have their different holidays schedule.Now i want to find that the current date is the business day or not(eliminate saturaday ,sunday and Holidays). tell me,Which one is feasible? Can i store the details of the holiday with description in 3 separate tables for 3 different centers or in a 3 separate file? is it possible to read the file using PL\SQl?

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