Question

My question regards how to design a database.

I have one table, called posts, with columns:

ID, subject, keywords, (and a few other columns)

and another table called keywords with:

kw_id, keyword.

Now, each “post” has several keywords and, sometimes, keywords are deleted because they don’t make sense or are duplicates.

My question is:

• Can keywords column in table posts be a foreign key? (each row will have multiple keywords)

• If I can’t, what is the best way to ensure data integrity (specially when a keyword is deleted)?

thanks in advance

EDIT: Can you point me any books or documents I should read about database design? It seems I’m laking key knowledge about database design.

Answer 1

You must flip dependencies: Table KEYWORD should reference back to post. You may want someting in between to find all posts for a given keyword (pseudo code):

POST
    POST_ID
    ...

KEYWORD
    KEYWORD_ID
    NAME        /* the keyword */

POSTKEYWORDREL    /* relationship */
    POST_ID     /* foreign key to POST */
    KEYWORD_ID  /* foreign key to KEYWORD */

Now you can easily delete a keyword from a given post by just removing the relationship in POSTKEYWORDREL.

EDIT: As always, for documentation let me point you to Wikipedia. You should also have a look at normalization (in my opinion the most important concept when it comes to database design).