COALESCE function in PLSQL

The COALESCE function take n arguments and produce the first argument, which has the first not null value.

i.e.

Select * from test;

A                      B                      C

-------                 -------                 -------

10                                             30

                        21                     31

12                     22                     32

                                                33

i.e.

Select c, coalesce(a,b,0) result from test;

C                      result

-------                 -------

30                     10        

31                     21

32                     12

33                     0