Question

I’m designing a database where any content can be tagged and I’m likely to want to be able to select all content with a specific tag.

I’m struggling with the following two options and would appreciate some advice. If there’s a better way please let me know.

Option A
Multiple ‘many to many’ join tables.

tag:
  id
  tag

media:
  id
  title
  src
  creation

media_tags:
  id
  media_id
  tag_id

article:
  id
  title
  content
  creation

article_tags:
  id
  article_id
  tag_id

Options B
A single ‘tag reference’ table, which uses a ‘table’ column to identify which table to join to.

tag:
  id
  tag

tag_reference:
  id
  row_id
  tag_id
  table

media:
  id
  title
  src
  creation

article:
  id
  title
  content
  creation

From a maintenance point of view option B seems favorable but considering the SQL query to select all content and don’t think it’s possible without multiple queries.

Answer 1

When using Option B, you can’t set up foreign keys to the other tables. Thus I would go with Option A and one table for each m:n relation.

“From a maintenance point of view option B” – is a nightmare. What happens if you delete an article? All the rows with that row_id will persist in tag_reference table. You always need to update those entries manually.