to_date function with sysdate

问题

select TO_CHAR(to_date(sysdate, 'DD-MON-YYYY'), 'DAY') FROM DUAL; 

When I run this query the output was : SUNDAY. But we know today is Tuesday(1-1-2013). And

then changed the query as

select TO_CHAR(to_date('01-JAN-2013', 'DD-MON-YYYY'), 'DAY') FROM DUAL;

answer was :TUESDAY.

then Changed query as

select TO_CHAR(to_date(sysdate+1, 'DD-MON-YYYY'), 'DAY') FROM DUAL;

answer is :MONDAY.

When I using the sysdate why it is show SUNDAY as output?

I am new in oracle db. Please help me.

回答1:

use this:

 select TO_CHAR(sysdate, 'DAY') FROM DUAL;

you are using this :

 to_date(sysdate, 'DD-MON-YYYY') 

which is giving you date=1/1/0013 which is sunday

回答2:

Please refer the documentation for sysdate here. Sysdate is already a date data type.

Your example query is inappropriate as to_date function takes first parameter as String not date.

Try the simple query below:

     select TO_CHAR(sysdate, 'DAY') FROM DUAL; 

This should return TUESDAY as output.

回答3:

To_date is used to convert a strin to date. As sysdate is already a date, one must not add add to_date.

来源：https://stackoverflow.com/questions/14108022/to-date-function-with-sysdate