DataCamp SQL_05 'Foreign keys'

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.

 

SELECT tag, COUNT(tag)

FROM stackoverflow

GROUP BY tag

HAVING COUNT(tag) > 1;