Oracle: explain NVL function?

Question

I know the nvl function only allows the same data type (i.e. number or char or date nvl(comm, 0)), if commission is null then the text “Not Applicable” want to display, instead of blank space. How do I write the query?

Answer 1

SQL> select nvl (to_char (comm.),'NA') from EMP; 

Output:

NVL (TO_CHAR (COMM),'NA')

NA
300
500
NA
1400
NA
NA