Tip of the Month (September 2001)
Multi-tiered Dependent Dropdowns with More than Four Levels
Dependent dropdowns allow you to restrict the selections in one dropdown based on what was selected in another. This is not limited to one level. They can be chained as deeply as you want (what you pick in A restricts B, what you pick in B restricts C, etc.). Detailed instructions on how to set this up can be found in the help topic "Multi-Tiered Dependent Dropdown Lists".
When setting up multi-tier dependent dropdowns, it is necessary to create indexes over columns in the support table. Since a table can only have four indexes, this causes a problem if you have more than four levels.
To resolve the problem, split the table into two tables. Once split, you can have four indexes per table (for a total of eight). If you need more, just split again.
For example, if you wanted to split the table in our Dealer/Make/Model/Year example, you could split the support table into two tables:
Note that one of the indexed columns would be in both tables.