You didn't say what version you are using, but FMP 11,
Manage > Value Lists
on the panel for Use values from field, right under the checkbox for
Show values from second field
is a pair of radio buttons, it reads
Sort values using: () First field () Second field
Click on the second field button
If you're using "show values only from second field" you are offered no choice but to sort by second field. RW
OMG, I didn't see the checkboxes, though I looked several times for a solution…
Anyway, thanks so much for your help.
Careful, this requires that the values in your second field be unique. If not, ID numbers will be omitted from your value lists when you sort on the second field.
Given the size of your value list, you may want to investigate options that use conditional value lists and/or scripts to present the user with a much shorter list of values.