Re: Virtual generated columns - Mailing list pgsql-hackers

On Wed, Sep 4, 2024 at 4:40 PM Peter Eisentraut <peter@eisentraut.org> wrote:
>
>
> Here is an implementation of this.  It's much nicer!  It also appears to
> fix all the additional test cases that have been presented.  (I haven't
> integrated them into the patch set yet.)
>
> I left the 0001 patch alone for now and put the new rewriting
> implementation into 0002.  (Unfortunately, the diff is kind of useless
> for visual inspection.)  Let me know if this matches what you had in
> mind, please.  Also, is this the right place in fireRIRrules()?

hi. some minor issues.

in get_dependent_generated_columns we can

            /* skip if not generated column */
            if (!TupleDescAttr(tupdesc, defval->adnum - 1)->attgenerated)
                continue;
change to
            /* skip if not generated stored column */
            if (!(TupleDescAttr(tupdesc, defval->adnum -
1)->attgenerated == ATTRIBUTE_GENERATED_STORED))
                continue;


in ExecInitStoredGenerated
"if ((tupdesc->constr && tupdesc->constr->has_generated_stored)))"
is true.
then later we finish the loop
(for (int i = 0; i < natts; i++) loop)

we can "Assert(ri_NumGeneratedNeeded > 0)"
so we can ensure once has_generated_stored flag is true,
then we should have at least one stored generated attribute.



similarly, in expand_generated_columns_internal
we can aslo add "Assert(list_length(tlist) > 0);"
above
node = ReplaceVarsFromTargetList(node, rt_index, 0, rte, tlist,
REPLACEVARS_CHANGE_VARNO, rt_index, NULL);



@@ -2290,7 +2291,9 @@ ExecBuildSlotValueDescription(Oid reloid,
if (table_perm || column_perm)
{
- if (slot->tts_isnull[i])
+ if (att->attgenerated == ATTRIBUTE_GENERATED_VIRTUAL)
+ val = "virtual";
+ else if (slot->tts_isnull[i])
    val = "null";
else
{
Oid  foutoid;
bool typisvarlena;
getTypeOutputInfo(att->atttypid, &foutoid, &typisvarlena);
val = OidOutputFunctionCall(foutoid, slot->tts_values[i]);
}

we can add Assert here, if i understand it correctly, like
 if (att->attgenerated == ATTRIBUTE_GENERATED_VIRTUAL)
{
Assert(slot->tts_isnull[i]);
 val = "virtual";
}