PLW-07204: conversion away from column type may result in sub-optimal query

Question

I have the following query in the package that created using sql developer. I am receiving the error 'PLW-07204: conversion away from column type may result in sub-optimal query plan' when try to compile the package. The issue is happen to be in the last line where the date is. Any help? Thanks
select count(*) into n_cnt
from tmp_order
where sgn_off_dt is null and cmt_dt is not null
and sysdate - cmt_dt > 90;

Answer 1

Sy:
Try doing as a procedure instead of an anonymous block. It looks like warnings do not apply to blocks.
SQL> create table tmp_order(sgn_off_dt date,cmt_dt date);
Table created.
SQL> alter session set plsql_warnings='ENABLE:ALL';
Session altered.
SQL> create procedure p as
  2     n_cnt number;
  3  begin
  4     select count(*) into n_cnt
  5     from tmp_order
  6     where sgn_off_dt is null and
  7           cmt_dt is not null and
  8           sysdate - cmt_dt > 90;
  9  end;
10  /
SP2-0804: Procedure created with compilation warnings
SQL> show err
Errors for PROCEDURE P:
LINE/COL ERROR
8/18     PLW-07204: conversion away from column type may result in
         sub-optimal query planlindalop:
In this case, you can ignore the warning, as it is not correct. Sysdate and a date column have different internal data types (note the type 13 for sysdate and type 12 for the date column), and whatever internally generates the warnings seems to just compare the type number.
SQL> insert into tmp_order values(sysdate, sysdate);
1 row created.
SQL> commit;
Commit complete.
SQL> select dump(sysdate) sdate, dump(cmt_dt) cmt_dt from tmp_order;
SDATE                             CMT_DT
Typ=13 Len=8: 7,219,2,3,15,44,4,0 Typ=12 Len=7: 120,111,2,3,16,44,12However, Oracle is perfectly capable of using an index on a date column with sysdate as a predicate. I would agree with Sy's suggestion to re-work the predicate to be something like cmt_dt < sysdate - 90.
John