ORACEL CASE WHEN 用法

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.

 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 ('.','.');

 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;