relational-database

How do I save multiple values in a single cell record in Ruby on Rails applications? If I have a table named Exp with columns named: Education , Experience , and Skill , what is the best practice if I want users to store multiple values such as: education institutions or skills in a single row? I'd like to have users use multiple text fields, but should go into same cell record. For instance if user has multiple skills, those skills should be in one cell? Would this be best or would it be better if I created a new table for just skills? Please advise, Thanks I would not recommend storing

I have a table with 2 fields (name, interest) and I want to find all pairs that have the same interest, with all duplicates and mirrored pairs removed. I am able to find all pairs and remove duplicates with the following SQL statement: SELECT P1.name AS name1, P2.name AS name2, P1.interest FROM Table AS P1, Table AS P2 WHERE P1.interest = P2.interest AND P1.name <> P2.name; But I am not sure how to remove mirrored pairs, ie: "wil","ben","databases" "ben","wil","databases" I tried to make the above statement a view called Matches and attempted the following query: SELECT * FROM Matches WHERE

I need to understand the difference between super key and composite key. The examples I found made more confused. Can you please simply clarify what is the difference? Thanks A super key uniquely identifies a row. It could be made up of one column or many. A composite key is a key made of more than one column. If a Super Key is made of more than one column it is also a composite. If a composite key uniquely identifies a row it is also a Super key. I don't see the name 'Super key' used too much: it's usually just called a 'Unique key'. The accepted answer is not entirely accurate... A superkey

I am implementing web application similar to Twitter. I need to implement 'retweet' action, and one tweet can by retweeted by one person multiple times . I have a basic 'tweets' table that have columns for: Tweets: tweet_id | tweet_text | tweet_date_created | tweet_user_id (where tweet_id is primary key for tweets, tweet_text contains tweet text, tweet_date_created is the DateTime when tweet was created and tweet_user_id is the foreign key to users table and identifies user who has created the tweet) Now I am wondering how should I implement the retweet action in my database. Option 1 Should I

I have to store scheduled events, (like say class times, for example) that can be organized on a weekly, daily or monthly basis. Events can occur, say, every Monday and Wednesday, or every second Thursday of the month. Is there a way to store this information in an RDBMS that adheres to 3NF? EDIT: This is not homework; I'm building something with a friend for our own edification and we want it in 3NF. To be specific, I'm trying to store the schedules for mass and confession times at RC parishes. These can be scheduled in a hell of a lot of ways, such as every Sunday at x time or every Tue/Thu