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

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;