SYSDATE is an Oracle only function.
The ANSI standard defines current_date or current_timestamp which is supported by Postgres and documented in the manual here.
(Btw: Oracle supports CURRENT_TIMESTAMP as well)
You should pay attention to the difference between current_timestamp, statement_timestamp() and clock_timestamp() (which is explained in the manual)
select up_time from exam where up_time like sysdate
Does not make any sense at all. Neither in Oracle nor in Postgres. If you need to get the rows from "today", you will have to use the following:
where up_time = current_date
Note that in the Oracle you would probably need trunc(up_time) = trunc(sysdate) to get rid of the time part which was always included in Oracle.
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