-- define a deferrable constraint allow check constraint when a transaction is commited, by default with immediate constraint allow check constraint after DML operation .
-- allow primary key check deferrable.
alter table t1 add constraint pk_t1 primary key (id) initially deferred ;
insert into t1 (id) values (1) ;
insert into t1 (id) values (1) ;
commit ; -- report error here.
-- allow foreign key check deferrable.
alter table t2 add constraint fk_t2_t1 foreign key (dept_id) referencing t1
initially deferred ;
insert into t2 (id,dept_id) values (1,999) ;
commit ; -- report error here.
-- switch constraint check at which points.
alter session set constraint=deferrable ;
set constraints all deferrable /immediate;
set constraint pk_t1 deferrable /immediate;
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