At 4:13 +0100 3/17/03, Andreas wrote:
RESTRICT is, of course, the default 'action'. ON DELETE and ON UPDATE are
later additions.
Paul DuBois wrote:
I see in the change notes that ON UPDATE was implemented in 4.0.8.
But how can ON DELETE be a later addition than RESTRICT? I was under the
impression that RESTRICT wasn't even implemented.
Also, the manual lists SET DEFAULT as a reference option for the general
CREATE TABLE syntax. Does that come into play for InnoDB at all?
As I get it, RESTRICT is no real "action" at all, since all it does
is watching the foreign key restriction to be followed.
That's an action in the sense that it prevents a parent table record
from being deleted.
ON DELETE was implemented because it makes sense and is actually
useful to safe some work.
What I meant is that because RESTRICT is one of the options for the
ON DELETE clause, you cannot implement RESTRICT *before* ON DELETE.
You cannot implement an option before the clause that it is an option *of*.
It makes sense to say that ON UPDATE was updated after ON DELETE, because
it was.
ON UPDATE seams to me to be more exotic since most foreign keys have
a primary key on one side, so the update target is a primary key,
which is not really elegant in my view.
Both actions DELETE and UPDATE have drawbacks if you have some
relations not covered by an explicit foreign-key-rule or if some
tables are still myisam.
Anyway RESTRICT is the core funtionality of foreign keys. Without it
FKs don't make much sense at all.
sql, query yada yada ...
--
Paul DuBois
http://www.kitebird.com/
sql, query
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