ORACLE 增加两列字段

declare v_cnt number;
 V_SQL VARCHAR2 (500) := \'\';
begin
 select count(*) into v_cnt from dual where exists(SELECT * FROM USER_TAB_COLUMNS WHERE TABLE_NAME = UPPER(\'TB_FDN_DEVICEACCOUNT\') AND COLUMN_NAME = \'NSBFL\');
   if v_cnt = 0 then
    V_SQL := \'ALTER TABLE TB_FDN_DEVICEACCOUNT ADD NSBFL NVARCHAR2(50)\';
    EXECUTE IMMEDIATE V_SQL;
    V_SQL := \'comment on column TB_FDN_DEVICEACCOUNT.NSBFL is \'\'原设备分类\'\'\';
    EXECUTE IMMEDIATE V_SQL;
end if;
 select count(*) into v_cnt from dual where exists(SELECT * FROM USER_TAB_COLUMNS WHERE TABLE_NAME = UPPER(\'TB_FDN_DEVICEACCOUNT\') AND COLUMN_NAME = \'NSBLX\');
   if v_cnt = 0 then
    V_SQL := \'ALTER TABLE TB_FDN_DEVICEACCOUNT ADD NSBLX NVARCHAR2(50)\';
    EXECUTE IMMEDIATE V_SQL;
    V_SQL := \'comment on column TB_FDN_DEVICEACCOUNT.NSBLX is \'\'原设备类型\'\'\';
    EXECUTE IMMEDIATE V_SQL;
end if;
end;