Is there an established pattern for SQL queries which group by a range?

I've seen a lot of questions on SO concerning how to group data by a range in a SQL query.

The exact scenarios vary, but the general underlying problem in each is to group by a range of values rather than each discrete value in the GROUP BY column. In other words, to group by a less precise granularity than you're storing in the database table.

This crops up often in the real world when producing things like histograms, calendar representations, pivot tables and other bespoke reporting outputs.

Some example data (tables unrelated):

|      OrderHistory       |       |         Staff        |                
---------------------------       ------------------------
|    Date    |  Quantity  |       |   Age     |   Name   |
---------------------------       ------------------------       
|01-Jul-2012 |     2      |       |    19     |   Barry  |
|02-Jul-2012 |     5      |       |    53     |   Nigel  |
|08-Jul-2012 |     1      |       |    29     |   Donna  |
|10-Jul-2012 |     3      |       |    26     |   James  |
|14-Jul-2012 |     4      |       |    44     |   Helen  |
|17-Jul-2012 |     2      |       |    49     |   Wendy  |
|28-Jul-2012 |     6      |       |    62     |   Terry  |
---------------------------       ------------------------

Now let's say we want to use the Date column of the OrderHistory table to group by weeks, i.e. 7-day ranges. Or perhaps group the Staff into 10-year age ranges:

|       Week      |  QtyCount  |        |  AgeGroup | NameCount |         
--------------------------------        -------------------------
|01-Jul to 07-Jul |     7      |        |   10-19   |    1      |
|08-Jul to 14-Jul |     8      |        |   20-29   |    2      | 
|15-Jul to 21-Jul |     2      |        |   30-39   |    0      |
|22-Jul to 28-Jul |     6      |        |   40-49   |    2      |
--------------------------------        |   50-59   |    1      |
                                        |   60-69   |    1      |
                                        -------------------------

GROUP BY Date and GROUP BY Age on their own won't do it.

The most common answers I see (none of which are consistently voted "correct") are to use one or more of:

• a bunch of CASE statements, one per grouping
• a bunch of UNION queries, with a different WHERE clause per grouping
• as I'm working with SQL Server, PIVOT() and UNPIVOT()
• a two-stage query using a sub-select, temp table or View construct

Is there an established generic pattern for dealing with such queries?