Greg Stark <gsstark(at)mit(dot)edu> writes:
> slo=> select '' order by 1;
> ERROR: Unable to identify an operator '<' for types '"unknown"' and '"unknown"'
> You will have to retype this query using an explicit cast
7.4 defaults this to type text:
regression=# select '' order by 1;
?column?
----------
(1 row)
regards, tom lane