newbie sql question: select every day another quote

for tutoral purpose i ve build a quotes table like this:

create table quotes (name text, quote text, lastdayshown date UNIQUE);
insert into quotes (name, quote) values ('caesar', 'veni vidi vici');
insert into quotes (name, quote) values ('hamlet', 'to be or not to be');

lastdayshown is always null on insert.
works fine. Now i want to select every day a different quote.

Is it possible to
select the row with lastdayshown = today
if no result
update one row with lastdayshown = null
else
update one row with oldest lastdayshown.

I want to put this procedural structure into sql, maybe creating a view, in
which the database user always sees the "Quote of the Day".

Maybe i am still thinking in procedural structures. Do i have to use PL/SQL
for it?

thanks in advance
janning

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