2016-03-17 0:39 GMT+01:00 Tom Lane <t...@sss.pgh.pa.us>: > 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 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. >
This is valid for PostgreSQL. I am not sure if it is true in Oracle, if %TYPE means only reference to type, or %TYPE holds reference to original object - and when you change the original object, then the function is invalidated. Using %TYPE with create time only semantic has not big practical benefit. But when %TYPE enforce all life dependency, then I have guaranteed so change on original object will be propagated to depend object. With all advantages and disadvantages. Postgres uses %TYPE in create time only semantic - but it is not big issue in PLpgSQL, because the creation time there is often - every first execution in session. The usage of %TYPE outer PL/pgSQL is probably only in FK. But nothing similar is in standard, and I don't see a reason, why we should to implement it. In this moment I don't see any important use case. Pavel > > regards, tom lane >
