How to fix ORA-12704: character set mismatch

Question

I am newish to oracle and am trying to work out why the following doesn't work:
create table utest(test nvarchar2(100));
insert into utest values('fish');
select test from utest union select '' from utest;
I need to be able to do a union on a table with an nvarchar2 fields, where on union, some of the columns are simply ''.
Not quite sure how to work out which oracle version exactly this is, we are given remote access via JDBC.

Answer 1

Hi
i have a similar issue on a customer. unfortunatly i am not able to modify the commands because i am not the developer. but i see in the logfile, that a ORA-12703 - Character Set Missmatch Occours after a specifiec command. after some investigation i found the command:
SELECT * FROM (SELECT DISTINCT ATTACHMENTID, FTN.USERID, FTN.MSGID, FTN.TYPEFLD, DS.DOCSERVERID, DOCSERVERPATH, DSTYPE,DSENABLED, DA.DATAARCHIVEID,FILENAME, STARTINGPOS, COMPRESSEDSIZE, UNCOMPRESSEDSIZE, MSGDATEHIGH,     MSGDATELOW, FLAGS, STORAGEMETHOD, SUBJECT, FROMFLD FROM CONTAINSATTACHMENT CA RIGHT JOIN FT_NOTIFY FTN ON CA.MSGID=FTN.MSGID , PROFILE P, PROFILELOCATION PL, DATAARCHIVE DA, DOCUMENTSERVER DS WHERE FTN.MSGID >= 547609 AND FTN.MSGID <= 557609 AND P.MSGID=PL.MSGID AND DS.DOCSERVERID=DA.DOCSERVERID AND DA.DATAARCHIVEID=PL.DATAARCHIVEID AND FTN.MSGID=P.MSGID AND FTN.SEARCH_INDEX_ID=2 AND TYPEFLD='A' UNION SELECT DISTINCT NULL AS ATTACHMENTID, FTN.USERID, FTN.MSGID, FTN.TYPEFLD,0 AS DOCSERVERID,'' AS DOCSERVERPATH,0 AS DSTYPE,0 AS DSENABLED,0 AS DATAARCHIVEID,'' AS FILENAME,0 AS STARTINGPOS,0 AS COMPRESSEDSIZE,0 AS UNCOMPRESSEDSIZE,0 AS MSGDATEHIGH,0 AS MSGDATELOW,-1 AS FLAGS, 0 AS STORAGEMETHOD,'' AS SUBJECT, '' AS FROMFLD FROM FT_NOTIFY FTN WHERE FTN.MSGID >= 547609 AND FTN.MSGID <= 557609 AND FTN.SEARCH_INDEX_ID=2 AND TYPEFLD='R') ORDER BY MSGID
when i replace the "'' AS..." in the bottom of the script with the "cast( '' as nvarchar(255)) AS..." it works as expected. as i sayd, i cant change the code but we have the system working for ages and after we set up a new server, it stops working - so can it be possible that other versions of Oracle (Server or Client) support this without a cast? Or is there some "Special Setting" what can help here?
Thank you in advance
Martin