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PostgreSQL 9 Administration Cookbook by Hannu Krosing, Simon Riggs

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Understanding object dependencies

In most databases, there will be dependencies between objects in the database. Sometimes, we need to understand those dependencies to figure out how to perform certain actions. Let's look at this in detail.

Getting ready

We'll use the following simple database to understand the issues and to 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 ...

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