These functions are the equivalent of the IF(x,T,F) function in the
ADBM formula language. The difference is that IFSTR(x,T,F) returns
a string result and IFNUM(x,T,F) returns a numeric result. All
three parameters x,T,F can be either string or numeric for both calls.
The SQL driver converts the value T or F that is returned to a string
for IFSTR and to a real number for IFNUM.