create table t1
(
 pkey integer not null,
 constraint pk_t1 primary key (pkey)
)

create table t2
(
 pkey integer not null,
 fkey integer,
 constraint pk_t2 primary key (pkey),
 constraint fk_t2 foreign key (fkey) references t1 (pkey)
)

alter table t2
drop constraint fk_t2

drop table t2  <<< Error