Oracle comment on的用法

Oracle comment on的用法

分类： 数据库相关技术 2011-09-07 16:46 1704人阅读 评论(1) 收藏 举报

oraclecommentstableusersqlmanager

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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