relational-database

I have got two tables: 1) Area 2) Map Each Area shall have at least 1 Map, but can also have more than one Map. One Map can only belong to one Area. How to build this in MySQL? Jenius Add a Foreign key in Map that references the Area's Primary Key. That will enforce a one-to-many relationship between Maps and Areas. As for enforcing a minimum of one map per area (if that is necessary) there are some ideas in this post here . One of the simpler solutions would be to create a view that only displays areas which have maps: CREATE VIEW viewAreas AS SELECT * FROM Areas, Maps WHERE Areas.ID = Maps

I have two SELECT statements in SQL Server like these: (SELECT [UserID] FROM [User]) (SELECT [TailUser], [Weight] FROM [Edge] WHERE [HeadUser] = 5043) I want to perform a LEFT JOIN between these two SELECT statements on [UserID] attribute and [TailUser] attribute. I want to join existent records in second query with the corresponding records in first query and NULL value for absent records. How can I do this? SELECT * FROM (SELECT [UserID] FROM [User]) a LEFT JOIN (SELECT [TailUser], [Weight] FROM [Edge] WHERE [HeadUser] = 5043) b ON a.UserId = b.TailUser SELECT [UserID] FROM [User] u LEFT

What is the advantage of defining a foreign key when working with an MVC framework that handles the relation? I'm using a relational database with a framework that allows model definitions with relations. Because the foreign keys are defined through the models, it seems like foreign keys are redundant. When it comes to managing the database of an application in development, editing/deleting tables that are using foreign keys is a hassle. Is there any advantage to using foreign keys that I'm forgoing by dropping the use of them altogether? Foreign keys with constraints(in some DB engines) give

As i couldnt get any satisfying answer to my Question it seems we have to write our own program for that, we are in the design phase and we are thinking which format shall we use to backup the data. The program will be written in Delphi. Needed is Exporting/Importing data between Oracle/Informix/Msserver, very important here is the Performance issue, as this program will run on a 1-2 GB Databases. Beside the normal data there are Blobs in the Database which have to be backuped. We thought of Xml-Data or comma-separated data as both are transparent (which is nice to have), but Blobs must be

Suppose I want to store relationships among the users of my application, similar to Facebook, per se. That means if A is a friend(or some relation) of B , then B is also a friend of A . To store this relationships I am currently planning to store them in a table for relations as follows UID FriendID ------ -------- user1 user2 user1 user3 user2 user1 However I am facing two options here: The typical case, where I will store both user1 -> user2 and user2->user1 . This will take more space, but (at least in my head) require just one pass over the rows to display the friends of a particular user.

I'm writing a mentorship program for our church in rails (im still farily new to rails).. And i need to model this.. contact has_one :father, :class_name => "Contact" has_one :mother, :class_name => "Contact" has_many :children, :class_name => "Contact" has_many :siblings, :through <Mother and Father>, :source => :children So basically an objects "siblings" needs to map all the children from both the father and mother not including the object itself.. Is this possible? Thanks Daniel It's funny how questions that appear simple can have complex answers. In this case, implementing the reflexive