Thank Lemming. It's always a possibility. And even if it is a homework
question, getting feed back can sometimes help one learn, though theres
no way to tell weather or not the OP was trying to take an easy way out
by just getting answers and running.

[snip]

Thanks to all those who replied, even to those who assumed it was a
homework question, but especially to Alfred. In fact, I am an
instructor, only recently assigned to teach databases, and I posted
the question for the benefit of a student who was asking me that
question. I did not put the question into a homework assignment! I
don't know the answer myself.

As for the comments that it uses a format popular with lecturers, I
have to say "of course". What else do you expect from a lecturer?

As for the comments suggesting I try it myself - I am not interested
so much in what a particular DBMS implements, since many don't follow
the standard. In fact, I told the student "you can try it yourself"
but cautioned that this would only illustrate the behaviour of a
particular DBMS, not the behaviour (if any) specified by the standard.

As for the comments that the person asking the question must be lazy
not to have tried to find the answer elsewhere - true. I didn't want
to spend half an hour wading through piles of sql technical
documentation when a quick query to google groups should unearth a
helpful person who can give the answer from memory in two minutes.

As for the suggestion to "provide your professor's email address",
well, I don't have a professor. My student's "professor", that is
yours truly, is an associate professor. My email address may be found
from the University's website. Look up : University Nottingham
Malaysia along with my name on google.

Now will someone please answer the question?

Yours, Mike H...