Re: plpgsql - DECLARE - cannot to use %TYPE or %ROWTYPE for composite types

On Wed, Mar 16, 2016 at 4:39 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

Jim Nasby <Jim.Nasby@BlueTreble.com> writes:
> On 3/3/16 4:51 AM, Pavel Stehule wrote:
>> CREATE TABLE a(a int);
>> CREATE TABLE b(a a.a%TYPE)
>>
>> And the people expecting the living relation between table a and table
>> b. So when I do ALTER a.a, then b.a should be changed. What if I drop
>> a.a or drop a?
>>
>> So this is reason, why I don't would this feature in SQL side.

> I don't buy that. plpgsql doesn't work that way, so why would this?
> *especially* with the %TYPE decorator.

Yeah.  The %TYPE decorator doesn't work like that in the core parser
either: when you use it, the referenced type is determined immediately
and then it's just as if you'd written that type name to begin with.

I'm missing something here...%TYPE ends up getting parsed repeatedly and so appears to be change if the variable upon which it is based changes - even if once parsed it remains constant for the lifetime of the function's evaluation.​

I guess what is being said is that the "constant" behavior in SQL ends up being permanent because a given statement is only ever conceptually parsed and executed a single time - unlike a function body.  The nature of any solution would still have the same characteristics within a function because the inherent re-parsing nature and not because of any direct capability of %TYPE itself.

I do not see a reason for any of these "type operators" to work
differently.

Another analogy that might help make the point is

        set search_path = a;
        create table myschema.tab(f1 mytype);
        set search_path = b;

If there are types "mytype" in both schemas a and b, is myschema.tab.f1
now of type b.mytype?  No.  The meaning of the type reference is
determined when the command executes, and then you're done.

​

And its no different than our treatment of "*"

CREATE VIEW test_view

SELECT *

FROM temp_table;

Adding columns to temp_table doesn't impact which columns the view returns.

David J.​