Question

SELECT * 
FROM CLIENT
WHERE CLIENT_REG_DATE > DATEADD(year,-1,GETDATE())
GROUPBY MONTH(CLIENT_REG_DATE).

I put into Apex Oracle and run it and it says

SQL command not properly ended

Answer 1

There is neither a DATEADD nor a getdate() nor a month() function in Oracle.

For a list of all available date functions, please refer to the manual:
http://docs.oracle.com/cd/E11882_01/server.112/e26088/functions002.htm#i88891

And statements have to be terminated with a ;

And if you are using SELECT * the group by is definitely not going to work either.

Without specifying in more detail what you want to group it’s hard to tell, but start with something like this:

SELECT to_char(client_reg_date, 'yyyy-mm'), count(*)
FROM CLIENT
WHERE CLIENT_REG_DATE > add_months(sysdate, -12)
GROUP BY to_char(client_reg_date, 'yyyy-mm')