java - 检查约束(或更好的东西)

Question

情况:有一个 java 应用程序从 DB Oracle 读取数据。为了简化，电子邮件字段当前是从“USERS”表中读取的。现在我必须修改应用程序，以便可以读取更多电子邮件地址，但我无意修改引用此表的所有数十个现有查询。欺骗行为是添加一个“EMAILS”表，其中(除了 PK“id_mailaddr”之外)仅包含“id_user”和“mail_address”字段。但因为数据不仅由应用程序加载，还由其他用户通过最多样化的方法(Excel 表、查询“插入全部”、sql 加载器等)加载，我必须在数据库级别强加一致性条件。问题就在这里!我不知道Oracle和PL-sql。如何编写“检查”约束来强加这样的约束:如果我在新表中插入的电子邮件地址的“id_user”已经存在于“USERS”表中，则该“id_user”在表“USERS”中匹配的电子邮件地址必须与新表中匹配的电子邮件地址一致？
例如:

USERS                                     EMAILS
id_user  user       email                 id_mailaddr   id_user  mail_address
100      Smith      smith@yahoo.com       1             100      smith@yahoo.com        OK!
101      Brown      brown@gmail.com       2             101      brown@gmail.com        OK!
102      M.Scott                          3             105      scott@hotmail.com      NO!
103      J.Scott    scott@hotmail.com     4             103      j_scott@hotmail.com    NO!
104      P.Scott                          5             104      scotty@aol.com         OK!

Answer 1

希望这个触发代码有帮助 -

drop table users;
drop table email;

CREATE TABLE users
    (id_user integer, userz varchar2(7), email varchar2(17))
;

INSERT ALL 
    INTO users (id_user, userz, email)
         VALUES (100, 'Smith', 'smith@yahoo.com')
    INTO users (id_user, userz, email)
         VALUES (101, 'Brown', 'brown@gmail.com')
    INTO users (id_user, userz, email)
         VALUES (102, 'M.Scott', '')
    INTO users (id_user, userz, email)
         VALUES (103, 'J.Scott', 'scott@hotmail.com')
    INTO users (id_user, userz, email)
         VALUES (104, 'P.Scott', '')
SELECT * FROM dual
;



CREATE TABLE email
    (id_mailaddr int, id_user int, mail_address varchar2(19))
;


insert INTO email (id_mailaddr, id_user, mail_address)
         VALUES (3, 105, 'scott@hotmail.com');

insert INTO email (id_mailaddr, id_user, mail_address)
         VALUES (5, 104, 'scotty@aol.com');         

create or replace trigger email_trig
after insert on email
for each row
declare
v_cnt integer := 0;
mail_adr varchar2(64);
e exception;
begin
    if inserting then
        select email, count(*) into mail_adr, v_cnt from users where id_user = :new.id_user group by email;

        if v_cnt = 0 or mail_adr <> :new.mail_address then
            raise e;
        end if;
    end if;
exception
    when others then
        raise_application_error(-20000, 'Error inserting new email:- '||:new.mail_address);
end;
/