For a non-"SELECT" statement, "execute" returns the
         number of rows affected, if known. If no rows were
         affected, then "execute" returns ""0E0"", which Perl
         will treat as 0 but will regard as true. Note that it is
         not an error for no rows to be affected by a statement.
         If the number of rows affected is not known, then
         "execute" returns -1.

Consider the following code:

while (my $rows = $dbh->do(<<SQL)) {
update #LAG
set tmpDate = dateadd( day, case
                when datepart( weekday, cl.tmpDate) = 2 then -3 else -
+1 end, cl.tmpDate)
from #LAG cl,
        $db..HOLIDAY h
where cl.tmpDate = h.Date
and cl.country = h.country
SQL
        print "$rows holidays adjusted\n";
}
[download]

This is Sybase, and I want to run the query repeatedly adjusting tmpDate in temporary table #LAG until none of them fall on holidays for the particular country. But, this code loops forever, as when there are no more rows, do returns "0E0".

I know that this subject has been covered before on PM, see Should string inequality operators return the point the of divergance? and What is truth? (Curiosity corner).

I also recall that the return value of the flip-flop operator .. in scalar context has "E0" appended to signal a terminating match. On some levels, I think that this is very clever, as this is interpreted by perl's string to number parser as "X 10 to the power 0". Hence, using this scalar value in numeric context gives you the line count.

I have several questions in my mind:

• Is this technique useful or just plain obscure?
• Could it be useful to have a truthful zero as return values elsewhere? Also, what's wrong with "00"?
• When does DBI return a "false" 0? Particularly when RaiseError is set to 1. Surely, DBI would then throw an exception if the query failed. Is there any advantage in false 0 over catching an exception with eval?

Update: I realise with hindsight that I hadn't made it clear that I had solved the original problem. This is the reason it was posted as a meditation, not SOPW.