Question

How would I set up a table for topics that a user likes? I have a topics tables and a user table (more actually but simplified for a post on here). There is an ever increasing number of topics as they are user generated, how could I allow users to like pages? Would i put the topic’s id in the user table or the user’s id in the topics table or a create a new likes table? The issue I see is that the number of topics could (potentially) be very large. What could I use to create a system that allows a relationship between a users id and the topics id?

Answer 1

What you could possibly do is a “many to many” table structure

• A unique auto incremented id – UINT (10) AUTO_INCREMENT
• A feild containing the user id – UINT (10) (or what ever matches your main user_id field)
• A field containing the “liked” topic id – UINT (10) (or what ever matches your main topic_id field)

Both user_id and topic_id fields would need to be unique together. That means that there can only be once row for a specific like per user. This makes sure (on the database side), that a user will not be allowed to like a topic more than once.

Getting a users liked topics would look like this –

SELECT * FROM user_likes` WHERE `user_id`=USER_ID

Getting the users per like would look like this –

SELECT * FROM user_likesWHEREtopic_id`=TOPIC_ID

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As others have said in their answers and also @trevor in the comments below –

Don’t forget to add an index on the userid to support retrieval of user liked topics and a separate index on topic is to support the topics per user query – without these, the queries will get slower as more data is added over time.