Questions about CURSORS

Hi,

Suppose there is a table that's being shared among 5
computers at the same time.
Suppose I've created a CURSOR for a SELECT * FROM
<that table> GROUP BY <column1>.
Suppose I have fetched the 3rd record and am going
to fetch the 4th and in the meantime someone at
another computer just DELETED that 4th record from
that table. Will the fetch succeed? Will the record
be shown although it no longer exists in the table?
And if someone at another computer had inserted a new
record which, according to my GROUP BY clause, would
be the 4th, would it be shown for the next fetch?
My big questions are: Do CURSORS perform their
SELECT operations in the TABLE directly or in a file?
Any changes to rows selected through a CURSOR will be
shown right away or they will only appear as I perform
another SELECT?
Is there a book that I could read in order to get a
better knowledge on SQL implementation or even a
website where I could read about this?

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