sql - Constraints interdependent tables -

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• are circular references acceptable in database? 8 answers

i created 2 tables dependent on each other this.

create table a(no1 number(2) primary key,no2 number(2)); 

table created.

create table b(no1 number(2) primary key,no2 number(2)); 

table created.

alter table add constraint aa foreign key(no2) references b(no1); 

table altered.

alter table b add constraint bb foreign key(no2) references b(no1); 

table altered.

insert values(10,20); insert values(10,20); 

error @ line 1: ora-02291: integrity constraint (subk.aa) violated - parent key not found

insert b values(10,20); insert b values(10,20); 

error @ line 1: ora-02291: integrity constraint (subk.bb) violated - parent key not found

how insert data in table a , b

you create invalid constraints:

 alter table b add constraint bb foreign key(no2) references b(no1); 

foreign key should different table, not column in same table.

if want circular constraint -> b , b ->a can insert first data , add constraints. foreign key should direct primary key, new sql :

create table a(no1 number(2) primary key,no2 number(2));      create table b(no1 number(2) primary key,no2 number(2));  insert values(10,20);   insert b values(10,20);  alter table add constraint aa foreign key(no1) references b(no1);  alter table b add constraint bb foreign key(no1) references a(no1);