In the documentation

http://www.python.org/dev/doc/devel/whatsnew/node7.html is written

about itertools.groupby:

"""Like it SQL counterpart, groupby() is typically used with sorted

input."""

In SQL queries is the groupby clause not related to 'input order'.

This notion makes not much sense in SQL context.

SQL is based on relational Algebra. A SQL- table is based on an

unordered set of rows (implementation can be different, of course).

So the analogon of

----------------------

import itertools

L = [2,4,6, 7,8,9,11, 12, 14]

for key_val, it in itertools.groupby(L, lambda x: x % 2):
.... print key_val, list(it)

....

0 [2, 4, 6]

1 [7]

0 [8]

1 [9, 11]

0 [12, 14]

------------------------

Say you have a table 'example' with only one column 'i'

_________________________

select * from example;

I

----

2

14

6

7

8

9

11

12

4

___________________________

the order of rows is not defined

Then you can group this table

____________________________________________

select count(i), mod(i,2) from example group by mod(i,2)

COUNT(I) | MOD(I,2)

---------+---------

6 | 0

3 | 1

___________________________________________

The result dos not depend on 'input order' or 'runs'