relational-database

I'm currently trying to design a database and I'm not too sure about the best way to approach a dynamically sized array field of one of my objects. My first thought is to use a column in my object to store an array of integers. However the more I read, the more I think this isn't the best option. Concrete example wise, I have a player object that stores 0 to many items, which are represented by an integer. What is the best way to represent this? If that collection of values is atomic , store them together. Meaning, if you always care about the entire group, if you never search for nested

I have three models: Book , genre , BookGenre , and here are relationships: class BookGenre < ActiveRecord::Base belongs_to :book belongs_to :genre end class Book < ActiveRecord::Base has_many :book_genres has_many :genres, through: :book_genres end class Genre < ActiveRecord::Base has_many :book_genres has_many :books, through: :book_genres end And then I use seed file to put data into these tables. But when I want to do rake db:seed again, it showed this error ActiveRecord::InvalidForeignKey: PG::ForeignKeyViolation: ERROR: update or delete on table "books" violates foreign key constraint

Once I use jdbc with oracle driver and run select query is the result of the query is stored in the server of oracle memory or file system or temp table ? and once I run the next method by getting the next row is it loaded from the oracle server memory to the jvm memory ? And in case I define the the number of fetch size on the result set to be 1000 is this mean that the 1000 rows are loaded from the oracle to the JDBC driver on the JVM? A default number of rows (not the entire result set) will be fetched in your local memory. Once you reach at the last line of the fetched rows (say by doing

I have a number of posts saved into a InnoDB table on MySQL. The table has the columns "id", "date", "user", "content". I wanted to make some statistic graphs, so I ended up using the following query to get the amount of posts per hour of yesterday: SELECT HOUR(FROM_UNIXTIME(`date`)) AS `hour`, COUNT(date) from fb_posts WHERE DATE(FROM_UNIXTIME(`date`)) = CURDATE() - INTERVAL 1 DAY GROUP BY hour This outputs the following data: I can edit this query to get any day I want. But what I want now is the AVERAGE of each hour of every day, so that if on Day 1 at 00 hours I have 20 posts and on Day 2

I am looking for how to build a relational mysql database, and I would like to follow a tutorial. I need one that shows how to make multiple tables, and link those together using an id. Which I can later use to grab relational data from the different tables. This is probably easy stuff, but I am just learning about databases. Thanks for the help! Here is a really good one for MySQL beginners. Nettus have some really great articles on Internet technologies. They are the new w3school. http://net.tutsplus.com/tutorials/databases/sql-for-beginners/ If you haven't already, I'd start with the MySQL