Questão de Informática

Considere um banco de dados no qual tenham sido executados os seguintes comandos SQL: drop table t3; drop table t1; drop table t2; create table t1 ( A int primary key, E int ); create table t2 ( B int primary key, D int not null ); create table t3 ( X int not null, Y int not null, Z int, constraint fk31 foreign key (X) references T1, constraint fk32 foreign key (Y) references T2, constraint uk31 unique(Y) ); insert into t1 values (10,8); insert into t1 values (11,9); insert into t1 values (12,5); insert into t2 values (2,5); insert into t2 values (4,8); insert into t2 values (5,6); insert into t3 values (10,2,20); insert into t3 values (10,4,null); insert into t3 values (12,5,30);