Mysql-> Group after rand() - mysql

Question

I have the following table in Mysql
Name Age Group
abel 7 A
joe 6 A
Rick 7 A
Diana 5 B
Billy 6 B
Pat 5 B
I want to randomize the rows, but they should still remain grouped by the Group column.
For exmaple i want my result to look something like this.
Name Age Group
joe 6 A
abel 7 A
Rick 7 A
Billy 6 B
Pat 5 B
Diana 5 B
What query should i use to get this result? The entire table should be randomised and then grouped by "Group" column.

Answer 1

What you describe in your question as GROUPing is more correctly described as sorting. This is a particular issue when talking about SQL databases where "GROUP" means something quite different and determines the scope of aggregation operations.
Indeed "group" is a reserved word in SQL, so although mysql and some other SQL databases can work around this, it is a poor choice as an attribute name.
SELECT *
FROM yourtable
ORDER BY `group`
Using random values also has a lot of semantic confusion. A truly random number would have a different value every time it is retrieved - which would make any sorting impossible (and databases do a lot of sorting which is normally invisible to the user). As long as the implementation uses a finite time algorithm such as quicksort that shouldn't be a problem - but a bubble sort would never finish, and a merge sort could get very confused.
There are also degrees of randomness. There are different algorithms for generating random numbers. For encryption it's critical than the random numbers be evenly distributed and completely unpredictable - often these will use hardware events (sometimes even dedicated hardware) but I don't expect you would need that. But do you want the ordering to be repeatable across invocations?
SELECT *
FROM yourtable
ORDER BY `group`, RAND()
...will give different results each time.
OTOH
SELECT
FROM yourtable
ORDER BY `group`, MD5(CONCAT(age, name, `group`))
...would give the results always sorted in the same order. While
SELECT
FROM yourtable
ORDER BY `group`, MD5(CONCAT(DATE(), age, name, `group`))
...will give different results on different days.

Answer 2

DROP TABLE my_table;
CREATE TABLE my_table
(name VARCHAR(12) NOT NULL
,age INT NOT NULL
,my_group CHAR(1) NOT NULL
);
INSERT INTO my_table VALUES
('Abel',7,'A'),
('Joe',6,'A'),
('Rick',7,'A'),
('Diana',5,'B'),
('Billy',6,'B'),
('Pat',5,'B');
SELECT * FROM my_table ORDER BY my_group,RAND();
+-------+-----+----------+
| name | age | my_group |
+-------+-----+----------+
| Joe | 6 | A |
| Abel | 7 | A |
| Rick | 7 | A |
| Pat | 5 | B |
| Diana | 5 | B |
| Billy | 6 | B |
+-------+-----+----------+

Answer 3

Do the random first then sort by column group.
select Name, Age, Group
from (
select *
FROM yourtable
order by RAND()
) t
order by Group

Answer 4

Try this:
SELECT * FROM table order by Group,rand()