What is the most efficient way to store tags in a database?

Question

I am implementing a tagging system on my website similar to one stackoverflow uses, my question is - what is the most effective way to store tags so that they may be searche

Answer 1

You can't really talk about slowness based on the data you provided in a question. And I don't think you should even worry too much about performance at this stage of developement. It's called premature optimization.

However, I'd suggest that you'd include Tag_ID column in the Tags table. It's usually a good practice that every table has an ID column.

Answer 2

If you don't mind using a bit of non-standard stuff, Postgres version 9.4 and up has an option of storing a record of type JSON text array.

Your schema would be:

Table: Items
Columns: Item_ID:int, Title:text, Content:text

Table: Tags
Columns: Item_ID:int, Tag_Title:text[]

For more info, see this excellent post by Josh Berkus: http://www.databasesoup.com/2015/01/tag-all-things.html

There are more various options compared thoroughly for performance and the one suggested above is the best overall.

Answer 3

Items should have an "ID" field, and Tags should have an "ID" field (Primary Key, Clustered).

Then make an intermediate table of ItemID/TagID and put the "Perfect Index" on there.

Answer 4

I'd suggest using intermediary third table for storing tags<=>items associations, since we have many-to-many relations between tags and items, i.e. one item can be associated with multiple tags and one tag can be associated with multiple items. HTH, Valve.

Answer 5

Actually I believe de-normalising the tags table might be a better way forward, depending on scale.

This way, the tags table simply has tagid, itemid, tagname.

You'll get duplicate tagnames, but it makes adding/removing/editing tags for specific items MUCH more simple. You don't have to create a new tag, remove the allocation of the old one and re-allocate a new one, you just edit the tagname.

For displaying a list of tags, you simply use DISTINCT or GROUP BY, and of course you can count how many times a tag is used easily, too.

Answer 6

If space is going to be an issue, have a 3rd table Tags(Tag_Id, Title) to store the text for the tag and then change your Tags table to be (Tag_Id, Item_Id). Those two values should provide a unique composite primary key as well.