CODEWITHSUNDEEP
mysql
Ben Hathaway
Ben Hathaway

Reputation: 356

Holding multiple items in a column on mysql

I am currently creating a database, it allows a user to upload a publication, which is stored in a table called paper, it stores the paper_id, title, abstract filename and topic_id .I have a table called topic which has topic_id and topic_name which i use for the user to select a topic for their publication. However i want the user to be able to select at least 3 topics, is this possible using this system? I have run out of ideas of how to do it and help would be greatly appreciated

Upvotes: 2

Views: 248

Answers (3)

Michael Berkowski
Michael Berkowski

Reputation: 270609

Don't store topic_id in the paper table. Instead, create another normalized (many-to-many) table which links topic_id to paper_id.

/* Each paper can exist in this table as many times as necessary for all its topics */
CREATE TABLE paper_topics (
  paper_id INT NOT NULL,
  topic_id INT NOT NULL,
  FOREIGN KEY (paper_id) REFERENCES paper (paper_id),
  FOREIGN KEY (topic_id) REFERENCES topic (topic_id),
  PRIMARY KEY (paper_id, topic_id)
);

This will allow you to store as many topics per paper as necessary.

To retrieve the topics for a paper, use:

SELECT 
  paper.*,
  topic_name
FROM 
  paper
  LEFT JOIN paper_topics ON paper.paper_id = topic.paper_id
  LEFT JOIN topic ON topic.topic_id = paper_topic.topic_id
WHERE paper.paper_id = <some paper id value>

It is just about never a good idea to attempt to store multiple values in one column (such as a comma-separated list of topic_id in the paper table). The reason is that in order to query against it, you must use FIND_IN_SET() which drives up the complexity of performing joins and makes it impossible to utilize a column index when querying.

Upvotes: 8

Mark Fraser
Mark Fraser

Reputation: 3198

Yes this is possible (using a separate table each for papers and topics). There would be a one to many relation between papers and topics.

http://www.databaseprimer.com/relationship_1tox.html

Upvotes: 0

Shomz
Shomz

Reputation: 37701

No problem, you can use serialization, like JSON.

Upvotes: 0

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