创建一个具有主键的表，该表与 oracle 中的现有表有一个可能的关系

Question

我有一个表 t1，其中包含许多以下记录

ID NAME TITLE ....

1  abc  X1
2  xyz  X1
3  qwe  X1
4  asd  X2
5  pqr  X2

我想创建一个新表 t2，它有一个主键，它在 t1 中引用了一个新的外键。此外，“标题”列的信息在 t2 中是不同的，因此，在 t2 中添加的任何记录都应反映在 t1 中，删除应从 t1 级联到 t2。

我做了以下事情：

create table t2 AS SELECT distinct (title) FROM t1;

ALTER TABLE t2
ADD (s_id,column1,column 2);

alter table t2 add primary key (s_id);

create sequence s_seq
start with 1
increment by 1
nomaxvalue;

update t2 set s_id=s_seq.nextval;


ALTER TABLE t1
add constraint fk_s_id
FOREIGN KEY (f_t2)
REFERENCES t2(s_id) on delete cascade;

这不适用于级联和插入。 请帮忙。

Answer 1

我错过了您如何创建 f_t2，它需要在某一时刻添加到 t1。所以我添加并填充了f_t2 列，它起作用了。

ALTER TABLE t1
ADD (f_t2 number);
update t1 set f_t2 = (select s_id from t2 where t2.title = t1.title);

运行以下产生了预期的结果。

drop table t1;
create table t1 (id number,name varchar2(100), title varchar2(100));
insert into t1 values (1, 'abc',  'X1');
insert into t1 values (2, 'xyz',  'X1');
insert into t1 values (3, 'qwe',  'X1');
insert into t1 values (4, 'asd',  'X2');
insert into t1 values (5, 'pqr',  'X2');
drop table t2;
create table t2 AS SELECT distinct (title) FROM t1;
ALTER TABLE t2
ADD (s_id number,column1 varchar2(10),column2 varchar2(20));
drop sequence s_seq;
create sequence s_seq
start with 1
increment by 1
nomaxvalue;
update t2 set s_id=s_seq.nextval;
alter table t2 add primary key (s_id);
ALTER TABLE t1
ADD (f_t2 number);
update t1 set f_t2 = (select s_id from t2 where t2.title = t1.title);
select * from t1;
select * from t2;
ALTER TABLE t1
add constraint fk_s_id
FOREIGN KEY (f_t2)
REFERENCES t2(s_id) on delete cascade;
delete from t2 where title='X2';
select * from t1;
select * from t2;

输出：

table T1 dropped.
table T1 created.
1 rows inserted.
1 rows inserted.
1 rows inserted.
1 rows inserted.
1 rows inserted.
table T2 dropped.
table T2 created.
table T2 altered.
sequence S_SEQ dropped.
sequence S_SEQ created.
2 rows updated.
table T2 altered.
table T1 altered.
5 rows updated.
        ID NAME                                                                                                 TITLE                                                                                                      F_T2
---------- ---------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------- ----------
         1 abc                                                                                                  X1                                                                                                            1 
         2 xyz                                                                                                  X1                                                                                                            1 
         3 qwe                                                                                                  X1                                                                                                            1 
         4 asd                                                                                                  X2                                                                                                            2 
         5 pqr                                                                                                  X2                                                                                                            2 

TITLE                                                                                                      S_ID COLUMN1    COLUMN2            
---------------------------------------------------------------------------------------------------- ---------- ---------- --------------------
X1                                                                                                            1                                 
X2                                                                                                            2                                 

table T1 altered.
1 rows deleted. --- DELETE in T2 affects T1
-- THIS IS T1:
            ID NAME                                                                                                 TITLE                                                                                                      F_T2
    ---------- ---------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------- ----------
             1 abc                                                                                                  X1                                                                                                            1 
             2 xyz                                                                                              

    X1                                                                                                            1 
             3 qwe                                                                                                  X1                                                                                                            1 
-- THIS IS T2:    
    TITLE                                                                                                      S_ID COLUMN1    COLUMN2            
    ---------------------------------------------------------------------------------------------------- ---------- ---------- --------------------
    X1                                                                                                            1