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oracle comment命令用法示例分享

来自:种豆 时间:2018-01-12 阅读:414次 原文链接

oracle中用comment on命令给表或字段加以说明,语法如下:


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.对表的说明


comment on table table_name is 'comments_on_tab_information';

2.对表中列的说明


comment on column table.column_name is 'comments_on_col_information';

3.查看表的说明


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


TABLE_NAME TABLE_TYPE COMMENTS
------------------------------ ----------- ----------
EMPLOYEES TABLE 员工表

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

TABLE_NAME TABLE_TYPE COMMENTS
------------------------------ ----------- --------------------------
EMPLOYEES TABLE 员工表

4.查看表中列的说明


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 员工薪水


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

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

5.我们也可以从下面这些视图中查看表级和列级说明:


ALL_COL_COMMENTS
USER_COL_COMMENTS
ALL_TAB_COMMENTS
USER_TAB_COMMENTS

6.删除表级说明,也就是将其置为空


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.删除列级说明,也是将其置为空


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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