How to use the case statement in Oracle

The CASE statement can be used in SQL for and IF-THEN-ELSE construction. It's an alternative for the decode statement and was introduced in Oracle 8. Syntax:
case( when condition then expr1 [when condition then expr2] ... [else exprN] ) end

Oracle searches for the first when condition that is true. The expr belonging the this condition is returned. If Oracle does not find such a condition, the expression belonging to the else statement is returned. If no else is specified the null value will be returned.

Sample code
select id
,      case (when status ='A' then 'Accepted'
             when status ='D' then 'Denied'
             else 'Other') end
from   contracts;

Will return for each id:
If status = 'A' : 'Accepted' 
If status = 'D' : 'Denied' 
Else            : 'Other'