oracle comment命令用法示例分享_Oracle

oracle comment命令用法示例分享

2019-12-03 15:32oracle教程网 Oracle

oracle comment on命令说明及用法示例，大家参考使用吧

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

复制代码代码如下:

comment on table table_name is 'comments_on_tab_information';

2.对表中列的说明

复制代码代码如下:

comment on column table.column_name is 'comments_on_col_information';

3.查看表的说明

复制代码代码如下:

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

复制代码代码如下:

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

复制代码代码如下:

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

复制代码代码如下:

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：

复制代码代码如下:

	
	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

复制代码代码如下:

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.删除列级说明，也是将其置为空

复制代码代码如下:

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