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oracle comment命令用法示例分享

更新時(shí)間：2013年12月31日 10:19:30 作者：

oracle comment on命令說明及用法示例，大家參考使用吧

oracle中用comment on命令給表或字段加以說明，語法如下：

COMMENT ON
  { TABLE [ schema. ]
    { table | view }
  | COLUMN [ schema. ]
    { table. | view. | materialized_view. } column
  | OPERATOR [ schema. ] operator
  | INDEXTYPE [ schema. ] indextype
  | MATERIALIZED VIEW materialized_view
  }
IS 'text' ;

用法如下：

1.對表的說明

復(fù)制代碼代碼如下:

comment on table table_name is 'comments_on_tab_information';

2.對表中列的說明

復(fù)制代碼代碼如下:

comment on column table.column_name is 'comments_on_col_information';

3.查看表的說明

復(fù)制代碼代碼如下:

SQL> select * from user_tab_comments where TABLE_NAME='EMPLOYEES';

復(fù)制代碼代碼如下:

TABLE_NAME TABLE_TYPE COMMENTS
------------------------------ ----------- ----------
EMPLOYEES TABLE 員工表

SQL> select * from user_tab_comments where comments is not null;

TABLE_NAME TABLE_TYPE COMMENTS
------------------------------ ----------- --------------------------
EMPLOYEES TABLE 員工表

4.查看表中列的說明

復(fù)制代碼代碼如下:

SQL> select * from user_col_comments where TABLE_NAME='EMPLOYEES';

復(fù)制代碼代碼如下:

TABLE_NAME                     COLUMN_NAME                    COMMENTS
------------------------------ ------------------------------ ------------
EMPLOYEES                      EMPLOYEE_ID
EMPLOYEES                      MANAGER_ID
EMPLOYEES                      FIRST_NAME
EMPLOYEES                      LAST_NAME
EMPLOYEES                      TITLE
EMPLOYEES                      SALARY                         員工薪水

SQL> select * from user_col_comments where comments is not null;

TABLE_NAME COLUMN_NAME COMMENTS
------------------------------ ------------------------------ -------------
EMPLOYEES SALARY 員工薪水

5.我們也可以從下面這些視圖中查看表級(jí)和列級(jí)說明：

復(fù)制代碼代碼如下:

ALL_COL_COMMENTS
USER_COL_COMMENTS
ALL_TAB_COMMENTS
USER_TAB_COMMENTS 

6.刪除表級(jí)說明，也就是將其置為空

復(fù)制代碼代碼如下:

SQL> comment on table employees is '';
Comment added

SQL> select * from user_tab_comments where TABLE_NAME='EMPLOYEES';

TABLE_NAME TABLE_TYPE COMMENTS
------------------------------ ----------- -------------
EMPLOYEES TABLE

7.刪除列級(jí)說明，也是將其置為空

復(fù)制代碼代碼如下:

SQL> comment on column employees.salary is '';
Comment added

SQL> select * from user_col_comments where TABLE_NAME='EMPLOYEES';

TABLE_NAME                     COLUMN_NAME                    COMMENTS
------------------------------ ------------------------------ -------------
EMPLOYEES                      EMPLOYEE_ID
EMPLOYEES                      MANAGER_ID
EMPLOYEES                      FIRST_NAME
EMPLOYEES                      LAST_NAME
EMPLOYEES                      TITLE
EMPLOYEES                      SALARY

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