Exercise

Foreign keys

Recall that foreign keys reference another row in the database via a unique ID. Values in a foreign key column are restricted to values in the referenced column OR NULL.

Using what you know about foreign keys, why can't the tag column in the tag_type table be a foreign key that references the tag column in the stackoverflow table?

Remember, you can reference the slides using the icon in the upper right of the screen to review the requirements for a foreign key.

Instructions

50 XP

Possible Answers

stackoverflow.tag is not a primary key
tag_type.tag contains NULL values
stackoverflow.tag contains duplicate values
tag_type.tag does not contain all the values in stackoverflow.tag