Only one entry "yes" in the whole table

[jaworski_m]

Hello,
I have a table with the following fields:

versionID (PK)
versionNumber
changeDescr
(...)
actualVersion ("Yes"/"No") - (text field)

I would like to set a validation rule at table level to make sure that there is only one entry [actualVersion]="Yes" in the whole table (the rest might be[actualVersion]="No")

I tried the following but did not work.

=DCount("[actualVersion]";"tblChangeLog";"[actualVersion] = 'Yes'")=1

How can I achieve this validation?

Thank you for hints.

[June7]

If it's a Yes/No type field, that is a Boolean. Boolean parameter is not text and should not be delimited with apostrophes.

=DCount("[actualVersion]", "tblChangeLog", "[actualVersion] = True")=1

However, I've never set validation rule at table level, no idea if domain aggregate function will work.

[jaworski_m]

This works:
http://stackoverflow.com/questions/2...t-most-one-yes