pl / sql中是否有BEFORE SELECT触发器？

Question

Hi I am using sqldeveloper conected to an oracle database.

My senario is I have a customer table in my database with a date field called start_date which holds the date of the day the user signed up and a "boolean" field called is_member . Each membership only lasts one year so is_member is false if SYSDATE > start_date + 1year .

I would like to do a check to see if a user is still a member (and change is_member if not) before the user calls a select statement. Is this possible?

If not has anyone got any ideas on how else to keep the is_member field up to date? Can you do a trigger that is called once a day to see if the membership has expiered?

Thanks in advace! =]

Answer 1

Don't use a table column to store dependent data, use a view:

CREATE OR REPLACE VIEW customer_v AS
SELECT c.*, 
       CASE WHEN SYSDATE > add_months(c.start_date, 12) 
          THEN 'FALSE' 
          ELSE 'TRUE' 
       END is_member
  FROM customer c

The is_member view column will always contain up-to-date data.

Answer 2

There is no such thing as a BEFORE SELECT trigger in PL/SQL.

It sounds like is_member should not be a column in a table at all but should be something that is computed in a view. Something like

CREATE OR REPLACE VIEW view_name
AS
  SELECT <<list_of_columns>>
         (CASE WHEN sysdate > add_months(start_date, 12)
               THEN 'Y'
               ELSE 'N'
           END) is_member
    FROM your_table

Your code would then simply query the view rather than querying the base table.

Answer 3

This is a job for the application to do the checking not a trigger. Triiger do not fire on SELECT.

As far as keeping the field up-to-date, there are two possibilities. First set up a nightly job to inactivate any members whose meberships have expired. Or change your struture to store membershipenddate rather than isactive and use that in the application check to see if the member is active.

Answer 4

You can add a Policy to your table and schema and Add the code that you want.

http://docs.oracle.com/cd/B28359_01/network.111/b28531/vpd.htm#CIHCAACD

CREATE OR REPLACE FUNCTION auth_orders( 
schema_var IN VARCHAR2,
table_var  IN VARCHAR2)
RETURN VARCHAR2
IS
return_val VARCHAR2 (400);
BEGIN
return_val := 'SALES_REP_ID = 159';
RETURN return_val;
END auth_orders;


BEGIN
DBMS_RLS.ADD_POLICY (
object_schema    => 'oe',
object_name      => 'orders',
policy_name      => 'orders_policy',
function_schema  => 'sys',
policy_function  => 'auth_orders',
statement_types  => 'select, insert, update, delete'
);
END;

Answer 5

您可以定义每天运行的作业并更新is_member字段。