Clob myClob = CLOB.createTemporary(sql.getConnection(), false, CLOB.DURATION_SESSION);
while ((row = reader.readNext()) != null) {

    myClob.truncate(0)
    myClob.setString(1,row[17])

        def stmt = /
                    MERGE INTO my_table a
                    USING (
                      SELECT    ${row[0]} id,
                                ${myClob} clob_column
                      FROM dual) e
                    ON (a.id = e.id)
                    WHEN MATCHED THEN
                      UPDATE SET
                            a.clob_column = e.clob_column

                      /

   def runsql = sql.execute(stmt)

${myClob ?: null}

${if(myClob.length() > 0) then myClob else null}