--- /dev/null
+UPDATE Transactions
+SET TimeTaken
+ = (CASE WHEN NewValue~E'^-?\\d+$' THEN NewValue::integer ELSE 0 END)
+ - COALESCE(OldValue::integer, 0)
+WHERE ObjectType = 'RT::Ticket' AND Type = 'Set' AND Field = 'TimeWorked';
\ No newline at end of file