Decode Statement Inside the Case statement

Question

Can we use Decode Statement inside a CASE Statement as show below --
It is giving an error -- Is the a better way to write with out any error
create or replace
function test (a varchar2) RETURN VARCHAR2
is
m varchar2(20);
begin
m :=
CASE
WHEN a IN (
'1009' -- (soon obsolete)
,'1010'
,'1019'
,'1051'
,'XGP'
,'XSC')
THEN (SELECT DECODE(v_lef_cd,'NAM','71','GLB','99','01') into m FROM DUAL)
-- ) THEN '01' -- UNITED STATES OF AMERICA
WHEN a IN (
'1069' -- South Africa
,'SAO' -- South Africa
,'SA' -- South Africa
) THEN '26' -- South Africa
ELSE NULL
END;
return m;
end;

Answer 1

Hi,
You can only use DECODE in SQL statements.
Your SELECT DECODE (...) INTO statement would work anywhere a PL/SQL statement is allowed; but PL/SQL statements are not allowed within CASE expressions.
Remember, the expression that comes after THEN in a CASE expression must be a single value.
I would write a function like this using IF ... ELSIF statements. It's a little more typing than CASE, but a lot easier to code, test and maintain.
If you want to use CASE, here's one way:
...     m := CASE
          WHEN  a  IN ('1069', 'SAO', 'SA')
               THEN  '26'     -- South Africa
          WHEN  a  NOT IN ('1009', '1019', '1051', 'XGP', 'XSC')
          OR    a  IS NULL
               THEN  NULL
          WHEN  v_lef_cd = 'NAM'
               THEN  '71'
          WHEN  v_lef_cd = 'GLB'
               THEN  '99'
               ELSE  '01'     -- USA
          END;This assumes that you have a variable v_lef_cd defined.
If you want, you can nest CASE expressions, like this:
...     m := CASE
          WHEN  a  IN ('1069', 'SAO', 'SA')
               THEN  '26'     -- South Africa
          WHEN  a  IN ('1009', '1019', '1051', 'XGP', 'XSC')
               THEN  CASE  v_lef_cd
                      WHEN  'NAM'
                         THEN  '71'
                      WHEN  'GLB'
                         THEN  '99'
                         ELSE  '01'     -- USA
                     END
          END;Always format your code, so you can see where the CASE expressions and each of the WHEN clauses begin and end.
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