Not a valid month in oracle when add_months is used

问题

I have given the below code in query.

    where to_date(cal_wid,'yyyymmdd') 
    between  add_months(to_date(sysdate, 'MM-YYYY'),-12) 
    and      to_date(sysdate, 'MM-YYYY')

I am getting the following bug. (I am doing in a Xampp server)

   Warning: oci_execute(): ORA-01843: not a valid month in C:\xampp\htdocs\xxx\index.php on line 149

   Warning: oci_fetch_array(): ORA-24374: define not done before fetch or execute and fetch in C:\xampp\htdocs\xxx\index.php on line 160

Can anyone tell why I am getting this error?

回答1:

Never, ever use TO_DATE() on something that is already a DATE. The reason for this is because Oracle will have to do some implicit conversions in order to follow your wishes:

TO_DATE(sysdate, 'mm-yyyy')

is really run as

TO_DATE(TO_CHAR(sysdate, '<default nls_date_format parameter>'), 'mm-yyyy')

so if your nls_date_format is set to something that's other than 'mm-yyyy', you're going to have problems. The default nls_date_format parameter is 'DD-MON-YY', which is more than likely the value yours is set to.

If all you wanted to do was to add_months to the 1st of the current month, then you should use TRUNC(), eg:

add_months(trunc(sysdate, 'MM'),-12)

Here's proof of the implicit to_char if you to_date something that's already a date, as requested by Lalit - an execution plan of a basic query involving to_date(sysdate):

SQL_ID  3vs3gzyx2gtcn, child number 0
-------------------------------------
select *  from   dual where  to_date(sysdate) < sysdate

Plan hash value: 3752461848

----------------------------------------------------------------------------
| Id  | Operation          | Name | E-Rows |E-Bytes| Cost (%CPU)| E-Time   |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |        |       |     2 (100)|          |
|*  1 |  FILTER            |      |        |       |            |          |
|   2 |   TABLE ACCESS FULL| DUAL |      1 |     2 |     2   (0)| 00:00:01 |
----------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter(TO_DATE(TO_CHAR(SYSDATE@!))<SYSDATE@!)

You can clearly see the TO_CHAR() in the filter condition.

来源：https://stackoverflow.com/questions/29141671/not-a-valid-month-in-oracle-when-add-months-is-used

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