Re: BUG #15198: nextval() accepts tables/indexes when adding a default to a column

On 16 May 2018 at 16:20, Peter Eisentraut
<peter.eisentraut@2ndquadrant.com> wrote:

> In this case, they are putting the erroneous call into a column default,
> so the difference ends up being getting the error at setup time versus
> at run time, which is a difference of significance.

Yes, I'm not particularly concerned with nextval taking a regclass as
an argument, and
therefore raising this error, but I'd rather have this error at DDL
time than at DML time.

I don't know how hard it would be to implement, but say, calling
currval(regclass) when
a default is defined should already throw this error at DDL time.

Or, when registering the default in the catalog, we verify that it is
actually a sequence:

Note: I'm not a C coder, so read it as pseudo-code please.

--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -2059,6 +2059,9 @@ StoreAttrDefault(Relation rel, AttrNumber attnum,
        defobject.objectId = attrdefOid;
        defobject.objectSubId = 0;

+       if (!IsSequence( find_oid_referenced (defobject) ) )
+               elog(ERROR, "Column defaults can only depend on sequences")
+
        heap_close(adrel, RowExclusiveLock);

        /* now can free some of the stuff allocated above */

but again, I've only seen this once, so the value of adding this check
seems very limited