Tatsuo Ishii <t-ishii@sra.co.jp> writes:
> test=# select (1,2,null) = (1,2,null);
> ERROR: Unable to identify an operator '=' for types 'unknown' and 'unknown'
> You will have to retype this query using an explicit cast
Well, there's no basis for deciding what the datatype of the third
column is.
The only reason you don't get the same error from the non-row case
regression=# select null = null;?column?
----------t
(1 row)
is that we have an ugly, horrible kluge in the parser to (mis) interpret
"foo = null" as meaning "foo ISNULL", in order to be compatible with
broken Microsoft SQL implementations. If you try any other operator
you get
regression=# select null <> null;
ERROR: Unable to identify an operator '<>' for types 'unknown' and 'unknown' You will have to retype this query
usingan explicit cast
I'd certainly not vote to propagate the "= null" kluge into the
row-equality code...
regards, tom lane