Best practice for storing tags in a database?

Question

I developed a site that uses tags (key words) in order to categorize photographs. Right now, what I have in my MySQL database is a table with the following structure:

Answer 1

You can make a tags table which is just an id and tag with a unique constraint on tag and then photo_tags table which has tag_id and photo_id. Insert a tag into the tags table only if it doesn't already exist.

Then you will be querying by a pk instead of varchar text comparison when doing queries like how many photos are tagged with a certain tag.