[Err] ORA-00923: FROM keyword not found where expected and rownum, ora-00923rownum

[Err] ORA-00923: FROM keyword not found where expected and rownum, ora-00923rownum
About oracle's nownum

If I want to query all the table information and add the row number in front of it, the SQL statement is as follows:

Select ROWNUM, * from tableA

The following error is reported.

[Err] ORA-00923: FROM keyword not found where expected

Alias must be added to the table.

Select rownum, a. * rownum from tableA

Why do you need this? I have not studied it in depth. Who knows? Please tell me.