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Optional Foreign Key Constraints?

DrDamnit
DrDamnit asked
on
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Last Modified: 2014-01-07
There are three tables: bugs, comments and attachments.

A comment is always associated with a bug. (bugs have comments).

An attachment will always be associated with a comment (attachments belong to specific comments)

BUT a comment will not always have an attachment. (Like cookies, attachments are a sometimes food).

How do I setup the foreign key constraints here?

Pretty sure this won't work because if I post a comment without an attachment, it will fail...

CONSTRAINT `fk_comments_bugs1`
    FOREIGN KEY (`comments_bug`)
    REFERENCES `bugreport`.`bugs` (`bugs_id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_comments_attachments1`
    FOREIGN KEY (`comments_attachment`)
    REFERENCES `bugreport`.`attachments` (`attachments_id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)

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North2AlaskaSenior Engineer
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Commented:
No, the FK is to prevent you from entering an attachment without a comment.  You should have no problem creating a comment without an attachment.
Data Warehouse / Database Architect
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Commented:
This one is on us!
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