I wrote:
> which are indeed different (might be worth looking into why)
Oh: the reason they're different is that these expressions are not
actually the same thing. Minus binds less tightly than typecast.
You get consistent results if you input equivalent expressions:
regression=# select cast(-1 as numeric(20,4));
numeric
---------
-1.0000
(1 row)
regression=# select (-1)::numeric(20,4);
numeric
---------
-1.0000
(1 row)
regression=# select - cast(1 as numeric(20,4));
?column?
----------
-1.0000
(1 row)
regression=# select - 1::numeric(20,4);
?column?
----------
-1.0000
(1 row)
What we're actually seeing here is that the code to guess a default
column name doesn't descend through a unary minus operator, it just
punts upon finding an Op node.
regards, tom lane