Introduction to SQL
A subquery in an SQL SELECT statement:

can always be duplicated by a join.
cannot have its results sorted using ORDER BY.
can only be used with two tables.
has a distinct form that cannot be duplicated by a join.

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Introduction to SQL
Which of the following query finds the name of the sailors who have reserved at least two boats?

All of these
SELECT DISTINCT s.sname FROM sailors s, reserves r1, reserves r2 WHERE s.sid = r1.sid AND COUNT(r1.bid) > r2.bid
SELECT DISTINCT s.sname FROM sailors s, reserves r1, reserves r2 WHERE s.sid = r1.sid AND r1.sid = r2.sid AND r1.bid <> r2.bid
SELECT DISTINCT s.sname FROM sailors s, reserves r1, reserves r2 WHERE s.sid = r1.sid AND r1.sid = r2.sid AND r1.bid ≠ r2.bid

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