relational-database

问题 The database looks like this: CREATE TABLE artists ( artist_id SERIAL PRIMARY KEY, artist TEXT UNIQUE NOT NULL ); CREATE TABLE artistalias ( artistalias_id SERIAL PRIMARY KEY, artist_id SERIAL REFERENCES artists (artist_id), alias TEXT UNIQUE NOT NULL ); CREATE TABLE songs ( song_id SERIAL PRIMARY KEY, song TEXT NOT NULL, artist_id SERIAL REFERENCES artists (artist_id) ); one artist can have zero, one or many aliases one alias belongs to exactly one artist one song has one artist one artist

问题 I am trying to develop a database to store data collected by a web based application that tracks employee activities. I have an employee table that looks like this Employee -------- id name position email And and multiple activity tables, each with different columns. An example of one: OutreachAndTraining ----- id date county city type ... ProfessionalDevelopment ------ id date comments I want to be able to keep track of which employees were a part of each activity but only want to log the

问题 I have an Article that have a creator and a modifier from User table. Here is the model: public class Article { public int ArticleId { get; set; } public string Name { get; set; } public int UserId { get; set; } public int ModifierId { get; set; } public virtual User User { get; set; } public virtual User Modifier { get; set; } } And here is the User model: public class User { public int UserId { get; set; } public string Username { get; set; } public string Password { get; set; } public

问题 This question is kind of a follow up to this question I asked a month ago. Here are my three tables. Fighters fighter_id | name ----------------------- 1 | John 2 | Steve 3 | Bill 4 | Bobby Events event_id | event_name | event_date ------------------------------------------- 1 | MMA | 01/01/2010 2 | Cool | 02/20/2010 3 | Yeaa! | 04/15/2010 Fights fight_id | fighter_a | fighter_b | winner | method | event ----------------------------------------------------------------------- 1 | 1 | 2 | 1 |

问题 I'm building a system that will auto-drop someone from one or more mailing lists, when they subscribe to another mailing list. I have a table 'lists' containing the list names. Each list will have one or more children in the form of 'exclusions', which are basically other lists. Here is my table: I'm wondering how best to achieve this. I originally thought of having another table called 'exclusions' linked via a lookup table with a many-to-many relationship, then I could grab all the

问题 E diagram which i need to turn into databse. I know my primary keys but do not really understand how to link the different tables together. So I have operator table with name as primary key. Each operator can operate certain proportion of those trains. e.g operator "a" 30 = 30% of those services and operator b 70% of those services 100 all of them etc... This is the part im stuck with. Do I need another table to link these two tables together ? for each train i need to store which station it

问题 I am working on a small web application that allows users to trade credit to each other. I would like to have your comments on my initial design (efficiency, flexibility, security etc.) In particular, a typical transaction happens as follow: User A can offer to do a job in exchange for X credits. Users B and C can accept the offer. A total of X credits will be subtracted from B and C's accounts. When the job is completed, X credits will be added to A's account. A can use earned credits to

问题 I encountered a problem to write this query in a Yii model oriented style. I have a 3 main tables : questions, categories, countries and relational tables : questions_has_categories, questions_has_countries. Now i try to search questions that belongs to country, category. With normal SQL statement i write : SELECT q.id, q.question, c.name, co.name FROM questions AS q, categories AS c, countries AS co, questions_has_countries AS ta, questions_has_categories AS qhc WHERE q.id = qhc.questions_id

问题 I have a table with the following possible values for the column field_value. But when I try to select all values which are not 'CB', the query result also ignores all NULL values. Why does this happen? mysql> select distinct field_value from TableName; +--------------+ | field_value | +--------------+ | S | | NULL | | CA | | CB | +--------------+ 4 rows in set (6.32 sec) mysql> select distinct field_value from TableName where field_value!='CB'; +--------------+ | field_value | +-------------

问题 Consider designing a database for the traffic department. There is a table for: violations, legalities, and drivers. In legalities table we have attributes for fine cost, clause number, explanation, reason, etc.... Now if we change the cost & clause number in future, I don't want this to affect the already existing records. But the tables violation and legalities are already in a relationship together, and hence this will change the old records if query for them. I gave a simple example to