Re: "JPPD bypassed: DISTINCT clause" in 19c

From: Sayan Malakshinov <>
Date: Sun, 6 Sep 2020 01:00:00 +0300
Message-ID: <>

Hi Nenad,

I'm sorry, I hadn't time to investigate it earlier. Just checked it and can confirm that Cost-based JPPD doesn't work with JSON_OBJECT, though Old-style OJPPD still works fine with it and pushes predicates without problems.
Do you need it exactly in new cost-based jppd?

>Do you have any workaround when JSON_OBJECT is in the select clause of the
main query block?
I've checked v$system_fix_control and haven't found anything related to this limitation.
I've tried many different variants: to pull it into parent views, wrap it into (select/*+ no_unnest */ ... from dual), but unfortunately the only workaround I found is to wrap it in your own user-defined function instead of JSON_OBJECT, for example:

  function json_x(xval int) return varchar2 as

     res varchar2(4000);

           'id' VALUE xval
           RETURNING VARCHAR2 (10)
           STRICT) as x
        into res
     from dual;
     return res;

select /*+ qb_name(QB_MAIN) */
 json_x(1) as x
  from t1 left outer join
    ( select /*+ qb_name(QB_MIDDLE) */ t2.n2
          t2  ,
         ( select  /*+ qb_name(QB_INNER ) */  t3.n2
            from t3, t4
            where   t4.n1 = t3.n1
         ) v2
        where  v2.n2(+) = t2.n1

    ) v1 on v1.n2 = t1.n1;

On Fri, Sep 4, 2020 at 4:08 PM Noveljic Nenad <> wrote:

> Thank you, Sayan.
> As opposed to your case, where you referenced json & co in the from
> clause, I used it only in the select clause.
> In this particular case, I don’t see any reason for bypassing JPPD –
> JSON_OBJECT is applied at the end.
> In fact, this used to work in 12c (tested on, but it
> doesn’t as of 18c (tested on and
> Do you have any workaround when JSON_OBJECT is in the select clause of the
> main query block?
> Best regards,
> Nenad
> *From:* Sayan Malakshinov <>
> *Sent:* Freitag, 4. September 2020 14:55
> *To:* Noveljic Nenad <>
> *Cc:* Andy Sayer <>; ORACLE-L (
> <>
> *Subject:* Re: "JPPD bypassed: DISTINCT clause" in 19c
> Hi Nenad,
> Yes, JPPD doesn't work in case of table(), XMLTABLE and JSON_TABLE:
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Best regards,
Sayan Malakshinov
Oracle performance tuning engineer
Oracle ACE Associate

Received on Sun Sep 06 2020 - 00:00:00 CEST

Original text of this message