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CASE WHEN [Oracle SQL]

case when x = y then a else b end

case when x < y then a when x = y then b else c end

case XYZ when 'foo' then 'moo' else 'bar' end
The following little SQL script demonstrates the use of CASE WHEN. 
create table test_case_when (
  a varchar2(5),
  b varchar2(5)
);

insert into test_case_when values ('*','*');
insert into test_case_when values ('+','+');
insert into test_case_when values ('-','-');
insert into test_case_when values ('.','.');

select a, 
  case
    when b = '*' then 'star'
    when b = '+' then 'plus'
    when b = '-' then 'minus' 
    else '????'
  end 
from test_case_when;
This select statement produces the following output: 
A     CASEW
----- -----
*     star
+     plus
-     minus
.     ????

drop table test_case_when;
See also decode.

Thanks

Thanks to William S. Cressman who notified me of an error on this page which is now corrected.