PRIVATE nIndex
nIndex=0

SELECT GetIndex() As recindex, *;
FROM customer;
WHERE postal_cde like 'J2K%';
HAVING empty(mod(recindex - 79, 7))

FUNCTION GetIndex() As Number
	nIndex=nIndex+1
RETURN nIndex 

This solution is probably less elegant, requires extra variable and function; but excludes RECNO() from the equation.