Sammenlign streng i Oracle Case When

Du kontrollerer strenge mod en tom streng, og har dermed problemer; i Oracle må du hellere tjekke om din streng is not null :

SELECT CASE WHEN '7C54D3E133830A78E040A8C010014B7D' is not null
            THEN '7C54D3E133830A78E040A8C010014B7D'
            WHEN 'e84a4433966c4b8996ce34905acff63d' is not null
            THEN 'e84a4433966c4b8996ce34905acff63d'
            WHEN '7faa9126b1c6412fa58375ab2b2be1db' is not null
            THEN '7faa9126b1c6412fa58375ab2b2be1db'
            ELSE NULL
 END
 FROM DUAL 

Om den måde, Oracle behandler tom streng og null på, her du finder noget mere

Et eksempel:

select q'['' = '']'         , case when '' = ''            then 'YES' else 'NO' end from dual union all
select q'['' is null]'      , case when '' is null         then 'YES' else 'NO' end from dual union all 
select q'['' = null ]'      , case when '' = null          then 'YES' else 'NO' end from dual union all 
select q'[null = null]'     , case when null = null        then 'YES' else 'NO' end from dual union all 
select q'[null is null]'    , case when null is null       then 'YES' else 'NO' end from dual union all 
select q'['' != '']'        , case when '' != ''           then 'YES' else 'NO' end from dual union all
select q'['' is not null]'  , case when '' is not null     then 'YES' else 'NO' end from dual union all
select q'['' != null ]'     , case when '' != null         then 'YES' else 'NO' end from dual union all
select q'[null != null]'    , case when null != null       then 'YES' else 'NO' end from dual union all
select q'[null is not null]', case when null is not null   then 'YES' else 'NO' end from dual

giver:

'' = ''           NO
'' is null        YES
'' = null         NO
null = null       NO
null is null      YES
'' != ''          NO
'' is not null    NO
'' != null        NO
null != null      NO
null is not null  NO

Kort sagt, den eneste check du kan stole på, når du taler om NULL , er:IS [NOT] NULL