Dynamic Menu Based on Decade

[jdadwilson]

I have a db table which contains information from HS yearbooks. One column of the table contains the year. Presently, I dynamically build a submenu containing all of the distinct years from the table. But, the list has now gotten rather long and I want to insert a second level submenu item with the decade. My problem is not building the submenus but rather determining the distinct decades needed.

Here is a link to the present submenu. Select the menu item... Windom Yearbooks and you will see the long list of years.

I would like to have something like this...

Windom Yearbooks >

'40s Yearbooks >

1949

'50s Yearbooks >

1950

Thus, my question relates to how to determine the distinct decades of the years from the db table.

TIA for your assistance
jdadwilson