在将字符串转换为日期时，某些列值可能为null，这不是有效的月份Oracle查询

Question

i have a query

SELECT DISTINCT ID 
  From ACCUSED 
 WHERE CAST(DATE_ENTERED AS date) BETWEEN '12-Apr-2013' and '12-Apr-2013'

This query show error "Not a valid month"

if i apply same query on my other table where string date is not null it works fine. This work fine

SELECT DISTINCT ID 
  From Customer 
 WHERE CAST(DATE_ENTERED AS date) BETWEEN '12-Apr-2013' and '12-Apr-2013'

Answer 1

Assuming that DATE_ENTERED is a VARCHAR2 column

1. You should never store a date as a string. A date should be stored in a DATE column. Using the wrong data type is the source of your problem and fixing the data model to use the correct data type is the proper solution.
2. If you want to convert a string to a date, us the TO_DATE function with an explicit format mask. A CAST or a TO_DATE with no format mask will cause whatever the session's NLS_DATE_FORMAT specifies as the format mask. Since that can be different for every session, that means that your code may work for some users from some clients and not work for other users or other clients and the bugs will inevitably be hard to find.
3. A DATE should always be compared to another DATE not to a string. Comparing a date to a string forces Oracle to do an implicit conversion which, again, uses the session's NLS_DATE_FORMAT and again makes your code unreliable. If you want to specify literal dates, either use the TO_DATE function to convert the string to a date (with an explicit format mask) or use an ANSI date literal
4. Assuming that ID is the primary key, the DISTINCT is, at best, meaningless and, at worst, forcing Oracle to do an unnecessary sort.

The first best solution is to modify the data model so that DATE_ENTERED is, in fact, a DATE . If you do that, your query becomes (using ANSI date literals)

SELECT id
  FROM accused
 WHERE date_entered BETWEEN date '2013-04-12' and date '2013-04-12'

or with an explicit TO_DATE

SELECT id
  FROM accused
 WHERE date_entered BETWEEN to_date( '12-Apr-2013', 'DD-Mon-YYYY' ) 
                        AND to_date( '12-Apr-2013', 'DD-Mon-YYYY' ) 

If, for some reason, you are stuck with the incorrect data model, if all the strings that you store are actually valid, you could do something like

SELECT id
  FROM accused
 WHERE to_date( date_entered, 'DD-Mon-YYYY' ) BETWEEN to_date( '12-Apr-2013', 'DD-Mon-YYYY' ) 
                                                  AND to_date( '12-Apr-2013', 'DD-Mon-YYYY' ) 

Given the error you are getting, however, it seems highly likely that there are at least some rows in the table where the string that has been stored in the table does not represent a valid date. The problem then becomes trying to figure out which rows are invalid. One option would be to create a new function

CREATE OR REPLACE FUNCTION my_to_date( p_date_str    IN VARCHAR2,
                                       p_format_mask IN VARCHAR2 )
  RETURN DATE
IS
  l_date DATE;
BEGIN
  l_date := to_date( p_date_str, p_format_mask );
  RETURN l_date;
EXCEPTION
  WHEN others THEN
    RETURN NULL;
END;

and then use that function in your query.

SELECT *
  FROM accused
 WHERE date_entered IS NOT NULL
   AND my_to_date( date_entered, 'DD-Mon-YYYY' ) IS NULL

will return all the rows where DATE_ENTERED does not represent a valid date in the format DD-Mon-YYYY . You'll have to correct this data eventually. If you are OK with ignoring any row with invalid data, you can write the query

SELECT id
  FROM accused
 WHERE my_to_date( date_entered, 'DD-Mon-YYYY' ) BETWEEN to_date( '12-Apr-2013', 'DD-Mon-YYYY' ) 
                                                     AND to_date( '12-Apr-2013', 'DD-Mon-YYYY' )