oracle 更改表添加列作为选择语句
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Alter table add column as select statement
提问by Kimaya
How to do something like this...
如何做这样的事情...
alter table customer_schedule add (week_number as (TO_CHAR((SCHEDULE_DATE),'iw'))
Wherein SCHEDULE_DATE is one of the existing columns in table
其中 SCHEDULE_DATE 是表中现有的列之一
回答by Lalit Kumar B
This is where you need VIRTUAL COLUMN. If you are on 11g and up, you could certainly do -
这是您需要VIRTUAL COLUMN 的地方。如果您使用 11g 或更高版本，您当然可以这样做 -
alter table table_name add (column_name [data_type] [generated always] as (column_expression) [virtual]);
In your case, it will be something like -
在您的情况下，它将类似于 -
alter table customer_schedule add (week_number data_type generated always as (TO_CHAR((SCHEDULE_DATE),'iw') VIRTUAL)
回答by René Nyffenegger
On 9i, you cannot use virtual columns, so I'd probably go with a view:
在 9i 上，您不能使用virtual columns，所以我可能会采用以下观点：
create view customer_schedule_view as
select
c.*,
to_char(c.schedule_date, 'iw')) week_number
from
customer_schedule c;
Of course, in your forms you need then to select from the view rather from the table.
当然，在您的表单中，您需要从视图而不是从表中进行选择。
回答by Sathyajith Bhat
The default keyword is supposed to let you store values when there is some value missing, but due to restrictions, you cannot use a column name
default 关键字应该让您在缺少某些值时存储值，但由于限制，您不能使用列名
A DEFAULT expression cannot contain references to PL/SQL functions or to other columns, the pseudocolumns LEVEL, PRIOR, and ROWNUM, or date constants that are not fully specified.
DEFAULT 表达式不能包含对 PL/SQL 函数或其他列、伪列LEVEL、PRIOR 和 ROWNUM 或未完全指定的日期常量的引用。
I think a row-level BEFORE INSERT/UPDATE trigger should do want you want to do.
我认为行级 BEFORE INSERT/UPDATE 触发器应该是你想做的。
