SQL & PL/SQL

db 12c, Apex 18.2, win 7.

Hi,

- I am trying to sort scott.emp table's data by hiredate column after I converted it to MM-YYYY format in the select list and added a group by clause.

SELECT
  TO_CHAR( hiredate, 'MM-YYYY' ) HIRE
FROM
  emp
GROUP BY
  TO_CHAR(HIREDATE,'MM-YYYY')
ORDER BY
 HIREDATE;

- It shows "ORA-00979: not a group by expression" when there is not a problem with the GROUP BY clause as the error is solved when removing the ORDER BY clause not the GROUP BY clause.

Edited:

1- Why the error?

2- How to sort the data correctly?

edited the title to be more specific: Eslam_Elbyaly