day_id(mm/dd/yyyy hh:mm:ss)

lalit it is typo error

cookiemonster day_id is the timestamp(6) and day_date is date

trunc(day_id) is working fine, thanks Littlefoot

SQL> select * from dual where sysdate=systimestamp;

no rows selected

Truncate the first (DAY_ID) column, and then join them, such as

where trunc(day_id) = the_second_date_column

SQL> select * from dual where trunc(systimestamp)=sysdate;

no rows selected

SQL> select * from dual where trunc(systimestamp)=trunc(sysdate);

D
-
X

depends on what's in the date column, doesn't it?

P.S. : Perhaps this is what Michel was pointing to.

depends on what's in the date column, doesn't it?

A DATE column also contains a time part (so is not "mm/dd/yyyy").
What kind of join do you actually want: up to second part or on day part?