Postgresql constraint

Question

I cannot seem to get this right, I am trying to modify a field to be a foreign key, with cascading delete... what am i doing wrong?

ALTER TABLE my_table ADD CONSTRAINT $4 FOREIGN KEY my_field REFERENCES my_foreign_table ON DELETE CASCADE;

Answer 1

Just guessing: shouldn't you add a foreign key instead of a constraint?

ALTER TABLE my_table ADD FOREIGN KEY (my_field) REFERENCES my_foreign_table;

Postgresql reference

Answer 2

It would help if you posted the error message. But I think you are just missing the parenthesis:

ALTER TABLE my_table ADD CONSTRAINT my_fk FOREIGN KEY (my_field) REFERENCES my_foreign_table ON DELETE CASCADE;