Good Morning Friends,I am new to this forum, I have recently joined Oracle DBA course and i have some basic doubts can you please clarify it

1)Unable to create a Duplicate table if the existing table contains the LONG datatype, What may b the reason ?

2) HAVING CLAUSE:
when we give condition in having clause in that condition we use some columns,group functions.Do this colum,Group function need to be present in SELECT,GROUP BY clause please do clarify dis doubt?

3) SYSDATE is a column or function because it doesnt use paranthesis?

4)As a DBA do we need to learn Shell Scripting, PL/SQL

Sorry friends for asking so many questions in my first post, please forgive me as we are here to learn