SQL表关系

Question

We have lots of tables in MS SQL that created without table relations many years ago. Now we are trying to create a relationship between these tables. The problem is in many of these developers used fake ids in the tables.

For example: TABLE A, ID(primary key) -> TABLE B, AID needs to be relational. But developers used some fake ids like -1,-2 to solve some problems in their side. And now when I try to create a relation between TABLE A, ID(primary key) -> TABLE B, AID, I am getting errors.

TABLE A

ID | NAME
1  | name01
2  | name02

TABLE B

ID | NAME   | AID
1  | name01 | 1
2  | name02 | -1
3  | name03 | -2

Is there way to solve this problem and is it meaning full what developers did, they didn't use any relations in sql, they are controlling everything in code-behind.

Thanks

Answer 1

You need to add those to your reference table. Something like this:

insert into a (id, name)
     select distinct aid, 'Automatically Generated'
     from b
     where not exists (select 1 from a where b.aid = a.id) and
           a.id is not null;

Then you can add the foreign key relationship:

alter table b add constraint fk_b_aid foreign key (aid) references a(id);

Answer 2

The general idea of referential integrity is exactly that you can't have invalid references.

So the best course of action here would be to suck it up and manually clean it up. Create the missing entries in the other table, or delete the records.

Answer 3

You can also ignore checks on existing data. If you are using sql server management studio to create relations there is option to do that just like in this screen shot

Hope it helps