oraclecomment命令用法示例分享

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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