oracle comment命令用法示例分享

湛蓝之海

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