ORA-00905: missing keyword in where case statement - sql

Question

select m_seqe
,m_emai
,m_phon
,e_seqe
,m_id
,
( case
when (:M_STAT = 0 ) and (m_id is not null ) then 'a'
when (:M_STAT = 0 ) and (m_id is null ) then 'b'
when (:M_STAT = 200 ) then 'c'
Else ' - ' end ) as Stat
from m_users
where m_stat = :M_STAT
and m_id =
case when (:M_ID = 0 ) then m_id is null
when (:M_ID ='a') then m_id is not null
else 'do nothing' end

Answer 1

The way you put it & I understood what you're saying, that would be a combination of several OR conditions:
WHERE m_stat = :M_STAT
AND ( ( m_id IS NULL AND :m_id = 0)
OR ( m_id IS NOT NULL AND :m_id = 'a')
OR ( m_id = 'do nothing'
);

Answer 2

You can't use a case expression to determine the logic in a filter; so this doesn't make sense and is what the parser is complaining about:
and m_id =
case when (:M_ID = 0 ) then m_id is null
when (:M_ID ='a') then m_id is not null
else 'do nothing' end
You could potentially have a case expression that evaluates to a value which you then compare against your column value, ut it doesn't seem to make sense here either, not least because null handling is a little awkward.
You seem to want to replace that with simple Boolean logic:
where m_stat = :M_STAT
and ((:M_ID = 0 and m_id is null)
or (:M_ID ='a' and m_id is not null))
or to be consistent in treating the bind variable as a string:
where m_stat = :M_STAT
and ((:M_ID = '0' and m_id is null)
or (:M_ID ='a' and m_id is not null))
There is no 'else' to worry about; your 'do nothing' string seems to be a placeholder that isn't intended to actually match against anything I.e. it's not a real m_id value you look for). If neither combined condition is true for a given row then the overall condition is false, and there won't be a match for that row and it will be filtered out.

Answer 3

Your problem is ambiguous but can be implemented as follows
select m_seqe
,m_emai
,m_phon
,e_seqe
,m_id
,
( case
when (:M_STAT = 0 ) and (m_id is not null ) then 'a'
when (:M_STAT = 0 ) and (m_id is null ) then 'b'
when (:M_STAT = 200 ) then 'c'
Else ' - ' end ) as Stat
from m_users
where m_stat = :M_STAT and
(
case when when (m_id IS NOT NULL AND :m_id = 'a') then 'a'
when (m_id IS NULL AND :M_ID = 0 ) then 'b'
when (m_id = 'do nothing') then 'c'
when 'd' end
) in ('a','b','c')