Need help with not exists

Can someone take a look at my not exists statement. I think it is hanging when I run my sql stored procedure.
Look at my not exists statement : IF NOT EXISTS(SELECT FUAD_ITS_CLERK_ID = @lchFITS_PREFIX + RandomId())
It does not look right to me, so maybe I just don't understand how to do it properly.


OPEN CURS_EMP
@lchFITS_SUFFIX= CONVERT(INT, @lchSuffix)
FETCH NEXT FROM CURS_EMP
INTO @lchPSUS_USER_NUM, @lchFITS_STATE_CD, @lchFITS_PREFIX
SELECT lchFITS_SUFFIX = @lchFITS_SUFFIX+1

WHILE @@FETCH_STATUS = 0
BEGIN
        SET @ClerkIdIsUnique = 0
        WHILE(@ClerkIdIsUnique = 0)
        BEGIN
             IF NOT EXISTS(SELECT FUAD_ITS_CLERK_ID = @lchFITS_PREFIX + RandomId())
            BEGIN
                     UPDATE SMT_FCTS_FUAD_TOPL_USR SET
                        FUAD_ITS_CLERK_ID =  @lchFITS_PREFIX + RandomId()
                         WHERE PSUS_USER_NUM = @lchPSUS_USER_NUM
                         AND (FUAD_ITS_CLERK_ID = @lchPSUS_USER_NUM
                     
                         UPDATE SMT_FCTS_FITS_STATE_CDS
                         SET FITS_SUFFIX = CONVERT(VARCHAR, @lchFITS_SUFFIX)
                         FETCH NEXT FROM CURS_EMP
                    INTO @lchPSUS_USER_NUM, @lchFITS_STATE_CD, @lchFITS_PREFIX
                         SET @ClerkIdIsUnique = 1
                         SELECT @lchFITS_SUFFIX = @lchFITS_SUFFIX+1
               END
               ELSE SELECT @lchFITS_SUFFIX = @lchFITS_SUFFIX+1
          END