Prevent Duplicate Insertion of Record

Question

I am trying to acheive some thing like this but i beleive
Insert Statement is not allowed in Case or Select is expecting some
thing in return that is why it keeps on giving me Missing
Expression . Is there any other way to prevent duplicate insertion
. i know we can do it by running another Query and then based on
recoundcount or count of that seperate query inserting records but
that i dont want to do .
SELECT CASE
WHEN ( SELECT COUNT(*) FROM THACARA WHERE ORG_CNY_CD = 'US'
AND ORG_REG_NR = '02' AND ORG_DIS_NR = '51') > 0
THEN (' DUPLICATE EXSIST')
ELSE (INSERT INTO THACARA ( USR_NR, ORG_FAC_LOC_NR, )
values ( 'Yousaf', 'FLIMI'))
END AS TEST FROM DUAL;
any ideas ??

Answer 1

It would be a lot better for everyone if you actually put a
unique constraint on your table rather than all this programming
(remember Oracle can have constraints). and preferably handle it in
a proper procedure and not injection - note that the "Answer" in
this thread does not actually return any information about whether
the record was inserted or not, just the actual record (nor does it
update the non-duplicate columns).
BEGIN
insert stuff
return 'inserted'
when DUP_VAL_ON_INDEX
update other stuff not making up the unique columns
return 'duplicate'
END