On Wed, Mar 16, 2016 at 4:39 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Jim Nasby <jim.na...@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.