sys@>set describe
SP2-0281: describe 缺失设置选项
用法:  SET DESCRIBE [DEPTH {1|n|ALL}] [LINENUM {ON|OFF}] [INDENT {ON|OFF}]
sys@>set describe linenum on
sys@>desc user_users;
           名称                            是否为空? 类型
           ------------------------------- -------- -------------------------

    1      USERNAME                        NOT NULL VARCHAR2(30)
    2      USER_ID                         NOT NULL NUMBER
    3      ACCOUNT_STATUS                  NOT NULL VARCHAR2(32)
    4      LOCK_DATE                                DATE
    5      EXPIRY_DATE                              DATE
    6      DEFAULT_TABLESPACE              NOT NULL VARCHAR2(30)
    7      TEMPORARY_TABLESPACE            NOT NULL VARCHAR2(30)
    8      CREATED                         NOT NULL DATE
    9      INITIAL_RSRC_CONSUMER_GROUP              VARCHAR2(30)
   10      EXTERNAL_NAME                            VARCHAR2(4000)

注意：作用就是为每行结果集产生一个行编号，这样有助于快速参考与比对