sql - 更改后如何知道列的先前长度

Question

我已经在Oracle中更改了列的大小，现在我想获取该列的上一个大小，因此无论如何我们都可以获取该列的上一个大小。

谢谢。

Answer 1

您可以在flashback上使用user_tab_columns:

SQL> conn <your_schema>
SQL> create table tab( str varchar2(20) );
SQL> alter table tab modify str VARCHAR2(30);
SQL> conn / as sysdba
SQL> grant flashback on user_tab_columns to <your_schema>;
SQL> conn <your_schema>
SQL> select *
  from user_tab_columns
 as of timestamp systimestamp - interval '1' minute c 
 where c.column_name = 'STR'
   and c.table_name = 'TAB'; 
-- the period depends on your latency of issuing the commands
-- "'1' minute" may be replaced with "'10' second" as an example.