Jcat
          寵辱不驚,閑看庭前花開花落~~
          posts - 173,comments - 67,trackbacks - 0

          Pseudo columns

          A pseudo column is an item of data which does not belong in any particular table but which can be treated as if it did. Any SELECT list of columns can include these pseudo columns.
          SYSDATE         current date and time
          
          ROWNUM          sequence number assigned to retrieved rows
          
          ROWID           unique identifier for a row
          
          UID             number associated with a user
          
          USER            userid of current user
          

          The DUAL table

          ORACLE provides a "dummy" table called DUAL containing one column and one row. It is useful for selecting miscellaneous information from ORACLE.

          Some uses for DUAL

          • Display today's date

            SELECT SYSDATE FROM dual;

          • Display the value of 356 divided by 17, to three decimal places

            SELECT ROUND(356 / 17, 3) FROM dual;

          • Display the current user name

            SELECT USER FROM dual;

          posted on 2006-08-18 08:50 Jcat 閱讀(240) 評論(0)  編輯  收藏 所屬分類: Database
          主站蜘蛛池模板: 江北区| 敦化市| 武宣县| 托克托县| 宣城市| 略阳县| 四子王旗| 和硕县| 丹江口市| 宁化县| 峨眉山市| 三原县| 基隆市| 琼中| 阳高县| 安福县| 安泽县| 北川| 青河县| 治多县| 子洲县| 汝州市| 大庆市| 石景山区| 错那县| 长宁县| 保德县| 沧源| 安庆市| 吉木乃县| 东方市| 大名县| 山东省| 灌云县| 勐海县| 靖州| 青冈县| 石门县| 凌云县| 平利县| 玛多县|