Oracle SQL convert date format from DD-Mon-YY to YYYYMM

问题

I have a to compare dates in 2 tables but the problem is that one table has the date in DD-Mon-YY format and the other in YYYYMM format.

I need to make both of them YYYYMM for the comparison.

I need to create something like this:

SELECT * FROM offers 
WHERE offer_date = (SELECT to_date(create_date, 'YYYYMM') FROM customers where id = '12345678') 
AND offer_rate > 0

where create_date is something like 12-Mar-2006 and offer_date is something like 200605

Any ideas where I need to adapt this query??

回答1:

As offer_date is an number, and is of lower accuracy than your real dates, this may work...
- Convert your real date to a string of format YYYYMM
- Conver that value to an INT
- Compare the result you your offer_date

SELECT
  *
FROM
  offers
WHERE
    offer_date = (SELECT CAST(to_char(create_date, 'YYYYMM') AS INT) FROM customers where id = '12345678')
AND offer_rate > 0 

Also, by doing all the manipulation on the create_date you only do the processing on one value.

Additionally, had you manipulated the offer_date you would not be able to utilise any index on that field, and so force SCANs instead of SEEKs.

回答2:

Am I missing something? You can just convert offer_date in the comparison:

SELECT *
FROM offers
WHERE to_char(offer_date, 'YYYYMM') = (SELECT to_date(create_date, 'YYYYMM') FROM customers where id = '12345678') AND
      offer_rate > 0 

来源：https://stackoverflow.com/questions/10536626/oracle-sql-convert-date-format-from-dd-mon-yy-to-yyyymm