relational-database
How to determine candidate keys from record schema and functional dependencies?
If I have a schema say R={A,B,C,D} and functional depen开发者_如何学Cdencies say {B->C, D->A} will my set of candidate keys be {B,D} or {BD}?If B were a candidate key, you\'d have to be able to[详细]
2023-04-08 22:37 分类:问答Which unique id to use for blogs and comments?
This is a question that arose from the consequences of another question here: Is it better to have two separate user tables or one?[详细]
2023-04-08 17:00 分类:问答Clear explanation of the "theta join" in relational algebra?
I\'m looking for a clear, basic explanation of the concept of theta join in relational algebra and perhaps an example (using SQL perhaps) to illustrate its usage.[详细]
2023-04-07 14:25 分类:问答EER : Superclass/subclass Entity relationship, primary key mapping
Here is the scenario. STUDENT, FACULTY are sub-classes ofPERSON entity, and they have specialized attributes.[详细]
2023-04-07 04:35 分类:问答Multivalued attributes in Relational databases?
How well an idea are multi-valued attributes in a relational database when they are to be referred extensively?[详细]
2023-04-06 09:56 分类:问答How should I use scope in Rails 3?
I have two models: First: class CountryList < ActiveRecord::Base has_one :country, :dependent => :nullify[详细]
2023-04-06 06:42 分类:问答Import XML file to create DB Schema and enter information
I have an XML file from a few datasets which I need to store in a Relational DB, say MySQL. The DB schema shld be created based on the fields of the XML file automatically.[详细]
2023-04-06 03:28 分类:问答Help with Grocery List Database design
I want to create a Grocery List Table that will accept both the Category and the Specific Products. For Example: I add to my grocery list:[详细]
2023-04-06 01:01 分类:问答How to store taxes in database?
I need to add per-province/state taxes to my project. I\'m debating whether I should add a many-to-many relationship between Provinces and Taxes, or just add a tax1_name, tax1_rate, tax2_name, tax2_r[详细]
2023-04-05 12:44 分类:问答how to use foreign keys as primary key
i have a table with two foreign keys as composite key. ActivityTbl - (activityNbr(PK), supervisor(FK), status, type, startDate, endDate, location )[详细]
2023-04-05 12:15 分类:问答