Postgresql limitation

Question

I can’t understand that this is correct, I am trying to change the field to be a foreign key, with cascading deletion ... 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

This will help if you post an 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; 

Answer 2

Just guess: should you add a foreign key instead of a restriction?

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

Postgresql Link

Answer 3

I still somehow missed the answer with an explicitly specified foreign column ( foreign_field ):

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

Answer 4

This works for me, I add a column to the table, and then add a constraint with links to another table:

 -- add column to table ALTER TABLE schema.table ADD COLUMN my_column type; -- add constraint to column ALTER TABLE schema.table ADD CONSTRAINT fk_name FOREIGN KEY (column) REFERENCES schema.table (column) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE NO ACTION;