Date to number conversion?

Question

I want to select a number of rows created within last week.
To do it I use a select statement with:
WHERE sysdate-o.created_on <= days;
(days is a number, created_on is a date)
Everything works fine, but I get warnings like this one:
PLW-07204: conversion away from column type may result in sub-optimal query plan
I suppose I should convert date to number to get rid of them. How can I do it isnide a SELECT query?

Answer 1

While the comments regarding re-writting the query to allow the possibility of index usage are valid, the warning will still appear even with the re-written query. I am sure that this query would use an index on dt1 if one was available.
SQL>CREATE TABLE t (id number, dt1 date, dt2 date);
Table created.
SQL> CREATE PROCEDURE p1 AS
  2  BEGIN
  3     FOR r IN (SELECT * FROM t
  4               WHERE dt1 = sysdate - 7) LOOP
  5        NULL;
  6     END LOOP;
  7  END;
  8  /
SQL>/
SP2-0804: Procedure created with compilation warnings
SQL>show error
Errors for PROCEDURE P1:
LINE/COL ERROR
3/13     PLW-07204: conversion away from column type may result in
         sub-optimal query planThe warning in this case is clearly spurious, and the reason is, at the level the compiler is looking, they are different data types. dt1 was inserted as sysdate a few minutes before I did the dunp below.
SQL> SELECT DUMP(dt1) tab_date, DUMP(dt1 - 3) calc_date,
  2         DUMP(sysdate) sys_date
  3  FROM t;
TAB_DATE                            CALC_DATE                          SYS_DATE
Typ=12 Len=7: 120,107,2,27,10,45,42 Typ=13 Len=8: 7,215,2,24,9,44,41,0  Typ=13 Len=8: 7,215,2,27,9,49,13,0A date field in a table is a type 12 while sysdate, and any date that has is a result of a calculation is a type 13. Clearly a "different" datatype.
Practically speaking, in the SQL engine, the type 13 date would be cast to a type 12 date and used in an index probe, but the compiler is likely doing something similar to the DUMP conparision.
I believe that the type 13 dates are a representation of the C time_t struct that Oracle's kernel would likely use internally.
John