May 2018
Intermediate to advanced
576 pages
30h 25m
English
We'll use the following simple database to understand and investigate them. There are two tables, as follows:
CREATE TABLE orders (orderid integer PRIMARY KEY);CREATE TABLE orderlines (orderid integer,lineid smallint,PRIMARY KEY (orderid, lineid));
Now, we add a link between them to enforce what is known as Referential Integrity, as follows:
ALTER TABLE orderlines ADD FOREIGN KEY (orderid)REFERENCES orders (orderid);
If we try to drop the referenced table, we get the following message:
DROP TABLE orders;ERROR: cannot drop table orders because other objects depend on itDETAIL: constraint orderlines_orderid_fkey on table orderlines depends on table ordersHINT: Use DROP ... CASCADE to drop the dependent objects too.
Be very careful! ...