Re: Virtual generated columns

[jian he]

in
transformColumnDefinition
we can add parser_errposition for the error report.
        if (column->is_not_null && column->generated ==
ATTRIBUTE_GENERATED_VIRTUAL)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("not-null constraints are not supported on
virtual generated columns"),
                     parser_errposition(cxt->pstate,
constraint->location)));
sometimes, it points to the word "generated", sometimes "not". I guess
this should be fine.
example:
create table t13 (a int, b bool generated always as ((true )) VIRTUAL not null);
create table t13 (a int, b bool not null generated always as ((true )) VIRTUAL);


These 3 functions will call StoreRelNotNull to store the not-null constraint.
StoreConstraints
AddRelationNotNullConstraints
AddRelationNewConstraints

we can disallow not-null on virtual generated columns via these 3 functions.
I guess we don't want to add more complexity to AddRelationNotNullConstraints.
we can do it in StoreRelNotNull.
like:
@@ -2185,8 +2196,19 @@ StoreRelNotNull(Relation rel, const char
*nnname, AttrNumber attnum,
 {
        Oid                     constrOid;
+       TupleDesc       tupdesc;
+       Form_pg_attribute att;
        Assert(attnum > InvalidAttrNumber);
+       tupdesc = RelationGetDescr(rel);
+       att             = TupleDescAttr(tupdesc, attnum - 1);
+
+       if (att->attgenerated == ATTRIBUTE_GENERATED_VIRTUAL)
+               ereport(ERROR,
+                               (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                                errmsg("not-null constraints are not
supported on virtual generated columns"),
+                                errdetail("Column \"%s\" of relation
\"%s\" is a virtual generated column.",
+
NameStr(att->attname), RelationGetRelationName(rel))));

related tests:
create table t12(b int, a int generated always as (11) virtual,
constraint nn not null a);
create table t12(b int, constraint nn not null a, a int generated
always as (11) virtual);

drop table if exists t14;
create table t14(b int, a int generated always as (11) virtual);
alter table t14 add constraint nn not null a;
alter table t14 add constraint nn not null a no inherit;