Introduction to SQL
In an SQL SELECT statement querying a single table, according to the SQL-92 standard the asterisk (*) means that:

all records meeting the full criteria are to be returned.
all records with even partial criteria met are to be returned.
all columns of the table are to be returned.
None of these

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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?

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
All of these

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Introduction to SQL
NULL is

not a value
the same as 0 for integer and blank for character
the same as 0 for integer
the same as blank for character

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