Need help with correcting the select statement

Question

I have two tables mkt & error.
The fields of mkt are
app_id (xxx)
c_mkt_id
app_mkt_id
The fields of error table are
mkt_id
intr_id (its in format xxx.yyy or xxx)
xyz
abc
pqr
I have to select * fields from error table such that
->mkt.app_id = error.intr_id (here i am using combination of sbstr & instr to get the part before "." if present)
->mkt.c_mkt_id=error.mkt_id
Where ever the above two conditions match i have to replace the mkt_id field in my select * from error table query with the
app_mkt_id field from mkt table. If the above two condtions dont match my select * from error table should return the original mkt_id present in the error table.
I have presently developed a query(*) which selects the app_mkt_id from mkt table where ever the two conditions match.
How should i go about using this to get my actual requirement.
(*)=select app_mkt_id from mkt where app_id in (select case when case_when=1 then substr(intr_id, 1, instr(intr_id,'.')-1) else substr(intr_id, 1) end from (select intr_id, case when instr(intr_id,'.',1)=0 then 0 else 1 end case_when from error)) and
c_mkt_id in (select mkt_id from error)

Answer 1

you wrote:
(*)=select app_mkt_id from mkt where ....What is this?
If you are writing PL/SQL the syntax is:
SELECT ....
INTO ....
FROM ....
WHERE ....This seems to be school work and thus you really need to puzzle this out for yourself.