oracle中用comment on命令給表或字段加以說明，語法如下：
復(fù)制代碼 代碼如下:
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和列級說明：
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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