Virtual Integrity

A recent question on the Oracle-L list server described a problem with data coming in from SQL Server and an oddity with referential integrity failing on Oracle because (for example) a child row was in lower case while the parent was in upper.

This raised a few comments on how you might handle referential integrity while allowed case to differ. No doubt it’s been done before – by Tom Kyte if no-one else – but the first thought that crossed my mind was to use virtual columns:

drop table child;
drop table parent;

create table parent (
	v1		varchar2(10) not null,
	padding		varchar2(100),
	v_pk		generated always as ( upper(v1)) virtual
);

alter table parent add constraint par_pk primary key(v_pk);

create table child (
	v1		varchar2(10) not null,
	padding		varchar2(100),
	v_ref		generated always as ( upper(v1)) virtual
);

alter table child add constraint chi_ref_par foreign key (v_ref) references parent(v_pk);

insert into parent (v1, padding) values ('ab',rpad('x',100));

insert into child  (v1, padding) values ('ab',rpad('x',100));
insert into child  (v1, padding) values ('Ab',rpad('x',100));
insert into child  (v1, padding) values ('aB',rpad('x',100));
insert into child  (v1, padding) values ('AB',rpad('x',100));

commit;

Prompt Expect ORA-00001 here:

insert into parent (v1, padding) values ('AB',rpad('x',100));

Obviously there are several details you’d have to check in the application to make sure that this strategy didn’t have any nasty side effects – does any of the code do an insert without referencing a column list, for example – but at first sight this looks like one way of matching incoming case-insensitivity “transparently”. You might still have reasons for creating case-insensitive indexes on the original columns, though, so I can’t claim that the method is virtually free.

Related posts:

1. Virtual Column
2. 展示单表外键信息的一个简单脚本
3. Forced Cursor Sharing And Virtual Columns
4. Forced Cursor Sharing And Virtual Columns
5. Exchange Partition, Virtual Columns And Column Statistics
6. SQL Gone Wild!
7. Exchange Partition, Virtual Columns And Column Statistics
8. SQL Gone Wild!
9. Separate Child Cursor with varying bind allocation length
10. Does the Parse Time Increase Linearly with the Number Of Child Cursors?