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Development Tools Database Foundations Joining Relational Data Between Tables in SQL Keys and Auto-Incrementing Values

Josh Jacobsen
Josh Jacobsen
2,445 Points

Trouble w/ Challenge Task in "Keys & Auto Incrementing Values" within "Joining Relational Data Between Tables in SQL"

Hi,

I'm having trouble writing the correct SQL for the following challenge task:

"Alter the "t_movies" table to add a foreign key called "fk_genre_id" and constrain it to reference the "t_genres" "pk_id"."

I've tried multiple SQL answers (below) and referenced both MySQL/WC3 documentation, can't seem to get it right:

1) ALTER TABLE t_movies ADD FOREIGN KEY fk_genre_id INTEGER, ADD CONSTRAINT FOREIGN KEY t_genres REFERENCES t_genres(pk_id) 2) ALTER TABLE t_movies ADD FOREIGN KEY fk_genre_id INTEGER NULL, ADD CONSTRAINT FOREIGN KEY t_genres REFERENCES t_genres(pk_id) 3) ALTER TABLE t_movies ADD COLUMN fk_genre_id INTEGER, ADD CONSTRAINT FOREIGN KEY t_genres REFERENCES t_genres(pk_id) 4) ALTER TABLE t_movies ADD COLUMN fk_genre_id INTEGER Null, ADD CONSTRAINT FOREIGN KEY t_genres REFERENCES t_genres(pk_id)

Error messages (matched w/ each of the above) are as follows: 1) -You're missing the 'fk_genre_id' column. -You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'INTEGER, ADD CONSTRAINT FOREIGN KEY t_genres REFERENCES t_genres(pk_id)' at line 1

2) -You're missing the 'fk_genre_id' column. -You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'INTEGER NULL, ADD CONSTRAINT FOREIGN KEY t_genres REFERENCES t_genres(pk_id)' at line

3) -You're missing the 'fk_genre_id' column. -You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'REFERENCES t_genres(pk_id)' at line 1

4) -You're missing the 'fk_genre_id' column. -You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'REFERENCES t_genres(pk_id)' at line 1

Assuming the answer's pretty simple but I'm still novice in my SQL abilities (outside of completing all Database Foundation work prior to this section).

Appreciate the help, thanks!

-Josh

1 Answer

Hi Josh, I also struggled with this challenge. The correct answer that i found via this answer in the forum is:

ALTER TABLE t_movies ADD COLUMN fk_genre_id INTEGER,
ADD CONSTRAINT FOREIGN KEY (fk_genre_id) REFERENCES t_genres(pk_id)

In my case I was missing the parenthesis around "fk_genre_id". It seems your answer (4) is closest to the correct answer and just needs to be updated after "FOREIGN KEY" and before "REFERENCES"!

Cheers, naano