@Tom Lane Yes, a good question. I abstracted my example to the point of meaninglessness. A more concreate example:
Create Type FOO(
F1 Int,
F2 Int,
...
Fn Int)
Create Function GET_SOMETHING(...) Returns SetOf FOO
Language PLPGSQL
...
Begin
...
Return Query
Select T1.T1F7 as F1, T2.T2F3 as F2, Tp.Fq as Fn
From T1 Join T2 On...Join...Tp
Where...
...
End;
This first example does not need the " as Fn" statements, they are just illustrative. The key problem here is that one needs to be certain that the order of the fields exactly matched the return type definition.
Another example would be a function in PLPGSQL that contains a loop:
Declare
_REC FOO;
Begin
for _REC In
Select ...name-based-constructor...
From T1 Join T2 On...Join...Tp
Where...
I'd like a formulation like:
Select Row(T1.T1F7 as F1, T2.T2F3 as F2, Tp.Fq as Fn)::FOO By Name
From T1 Join T2 On...Join...Tp
Where...
Or
Select FOO(F1:=T1.T1F7, F2:=T2.T2F3, Fn:=Tp.Fq)
From T1 Join T2 On...Join...Tp
Where...
Or any other syntax that can be consistent, not break function calling etc
Basically: it's some form of UDT constructor with named parameters, whether by cast, pseudo function call or some other mechanism.
This also allows plain SQL to return UDTs reliably and consistently.
I really hope these example makes the intent clearer!
On 2025-09-05 15:54, Tom Lane wrote:
Philip Warner <
pjw@rhyme.com.au> writes:
The Problem
Currently, if one has:
Create Type FOO(
VALUE1 Int,
VALUE2 Int);
And one has a query:
Select F1, F2 from A_TABLE;
One can return the rows, or one can create a row object and cast it to
FOO type.
I'm kind of wondering where is the connection between type FOO and
table A_TABLE?
Once you have the table, there is already a perfectly good composite
type A_TABLE that you could use without any worries about whether it
matches the table. So I'm not following why introducing FOO adds
anything of value.
regards, tom lane
