how to save tags(keywords) in database?

Question

I want to create a simple tags system using php and mysql, so that users can add few tags via form. My question is that should i save the tags as an array in single database col

Answer 1

I would probably say neither. Use a many-to-many relationship between tags and the object being tagged. For instance, if the thing being tagged is a question, the tables could look like this:

Question:
    QuestionId
    Title
    Body

Tag:
    TagId
    Name

QuestionTags:
    QuestionId
    TagId