Q:

In SQL, what does Group By mean without Count(*), or Sum(), Max(), avg(), ..., and what are some uses of it?

In SQL, if we use Group By without Count(*) or Sum(), etc, then the result is as follows:
mysql>  select * from sentGifts;
+--------+------------+--------+------+---------------------+--------+
| sentID | whenSent   | fromID | toID | trytryWhen          | giftID |
+--------+------------+--------+------+---------------------+--------+
|      1 | 2010-04-24 |    123 |  456 | 2010-04-24 01:52:20 |    100 |
|      2 | 2010-04-24 |    123 | 4568 | 2010-04-24 01:56:04 |    100 |
|      3 | 2010-04-24 |    123 | NULL | NULL                |      1 |
|      4 | 2010-04-24 |   NULL |  111 | 2010-04-24 03:10:42 |      2 |
|      5 | 2010-03-03 |     11 |   22 | 2010-03-03 00:00:00 |      6 |
|      6 | 2010-04-24 |     11 |  222 | 2010-04-24 03:54:49 |      6 |
|      7 | 2010-04-24 |      1 |    2 | 2010-04-24 03:58:45 |      6 |
+--------+------------+--------+------+---------------------+--------+
7 rows in set (0.00 sec)

mysql>  select *, count(*) from sentGifts group by whenSent;
+--------+------------+--------+------+---------------------+--------+----------+
| sentID | whenSent   | fromID | toID | trytryWhen          | giftID | count(*) |
+--------+------------+--------+------+---------------------+--------+----------+
|      5 | 2010-03-03 |     11 |   22 | 2010-03-03 00:00:00 |      6 |        1 |
|      1 | 2010-04-24 |    123 |  456 | 2010-04-24 01:52:20 |    100 |        6 |
+--------+------------+--------+------+---------------------+--------+----------+
2 rows in set (0.00 sec)

mysql>  select * from sentGifts group by whenSent;
+--------+------------+--------+------+---------------------+--------+
| sentID | whenSent   | fromID | toID | trytryWhen          | giftID |
+--------+------------+--------+------+---------------------+--------+
|      5 | 2010-03-03 |     11 |   22 | 2010-03-03 00:00:00 |      6 |
|      1 | 2010-04-24 |    123 |  456 | 2010-04-24 01:52:20 |    100 |
+--------+------------+--------+------+---------------------+--------+
2 rows in set (0.00 sec)

Only 1 row is returned per "group".  What does it mean when there is no "Count(*)", etc when using "Group By", and what are it uses?  thanks.

A:

By default, MySQL will return the value of the first row it encounters when executing the query.  It's like it uses a default aggregate of arbitrary.
This is useful if you have a long column list where you know most of them are repeating, for example:
Login    LongName             City        PhoneNr      Time
Dude     Mr. Dude the 2nd     Jerk Town   12345678     13:01
Dude     Mr. Dude the 2nd     Jerk Town   12345678     13:05
Dude     Mr. Dude the 2nd     Jerk Town   12345678     13:12

Here you could group by login:
select LongName, City, PhoneNr, max(Time) from Logins group by login

Because you know that Long Name depends on Login, this will work as expected.  All other DBMS systems I know of require you to explicitly specify group by login, LongName, City, PhoneNr. Even in MySQL that is considered good practice.

