This might be a trivial question. And I didn't find much of the discussion after googling the topic. But I am still debating of picking a default value for foreign key column to represent the non- existence of such fk.
Is there any advantage between using NULL vs. using 0? What are the pros and cons? What do you guys use as a convention?
Will using 0s reducing table size in terms of storage?
On Tue, 3 Nov 2009 14:36:51 -0800 (PST), Devy wrote: > This might be a trivial question. And I didn't find much of the > discussion after googling the topic. But I am still debating of > picking a default value for foreign key column to represent the non- > existence of such fk.
> Is there any advantage between using NULL vs. using 0? What are the > pros and cons? What do you guys use as a convention?
Null's an *automatic* special case, that contaminate the specialness to other operations automatically. 0 you have to code a lot of checking for yourself. For example, null records cannot possibly join to anything. A zero foreign key joins to any record that HAPPENS to end up with a zero value in the referenced field, and if you default THAT to zero as well, well... let's just say it's REALLY EASY to end up with a lot of records that match that you don't want to.
> Will using 0s reducing table size in terms of storage?
Not by any appreciable amount. Disk is *cheap*.
-- 62. I will design fortress hallways with no alcoves or protruding structural supports which intruders could use for cover in a firefight. --Peter Anspach's list of things to do as an Evil Overlord
> This might be a trivial question. And I didn't find much of the > discussion after googling the topic. But I am still debating of > picking a default value for foreign key column to represent the non- > existence of such fk.
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