my $transactiontime = "
CASE Transactions.Type WHEN 'Set'
- THEN (TO_NUMBER(NewValue,'999999')-TO_NUMBER(OldValue, '999999')) * 60
+ THEN ( CASE WHEN NewValue = '' THEN 0 ELSE TO_NUMBER(NewValue,'999999') END
+ -TO_NUMBER(OldValue, '999999')
+ ) * 60
ELSE TimeTaken*60
END
";