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

2016-03-17 1:02 GMT+01:00 David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>:

> On Wed, Mar 16, 2016 at 4:39 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)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.
>

yes, but there is strong limit. You can append column, but you cannot to
alter existing column.

Pavel

>
> David J.​
>
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