Oracle 18c

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alter session set nls_date_format = 'YYYY-MM-DD HH24:MI:SS';
create table T ( 
  n int,
  dt DATE,
  constraint t_chk check (dt=trunc(dt, 'dd')),
  constraint t_pk primary key (n, dt)
);
insert into t (n, dt) values (1, to_date('2020-06-29 12:34:56', 'YYYY-MM-DD HH24:MI:SS'));
ORA-02290: check constraint (FIDDLE_NAHODXMKBJHFRAXTGDNA.T_CHK) violated

insert into t (n, dt) values (1, to_date('2020-06-29 00:00:00', 'YYYY-MM-DD HH24:MI:SS'));
1 rows affected

insert into t (n, dt) values (1, to_date('2020-06-29 00:00:00', 'YYYY-MM-DD HH24:MI:SS'));
ORA-00001: unique constraint (FIDDLE_NAHODXMKBJHFRAXTGDNA.T_PK) violated

select * from t;


N
DT


1
2020-06-29 00:00:00


drop table t;
create table T ( 
  n int,
  dt DATE,
  dd DATE generated always as (trunc(dt)),
  constraint t_pk primary key (n, dd)
 );
insert into t (n, dt) values (1, to_date('2020-06-29 12:34:56', 'YYYY-MM-DD HH24:MI:SS'));
1 rows affected

insert into t (n, dt) values (1, to_date('2020-06-29 00:00:00', 'YYYY-MM-DD HH24:MI:SS'));
ORA-00001: unique constraint (FIDDLE_NAHODXMKBJHFRAXTGDNA.T_PK) violated

select * from t;


N
DT
DD


1
2020-06-29 12:34:56
2020-06-29 00:00:00


drop table t;