Oracle 21c

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create table TA (  
  TA_1          number,  
  constraint pk_departments primary key (TA_1)  
);
create table TB (  
  TB_1          number,  
  constraint fk_TA foreign key (TB_1)
  REFERENCES TA(TA_1)
);
INSERT INTO TA (TA_1)
   VALUES (1);
1 rows affected

INSERT INTO TA (TA_1)
   VALUES (2);
1 rows affected

INSERT INTO TA (TA_1)
   VALUES (3);
1 rows affected

INSERT INTO TB(TB_1)
   VALUES (1);
1 rows affected

INSERT INTO TB(TB_1)
   VALUES (2);
1 rows affected

INSERT INTO TB(TB_1)
   VALUES (3);
1 rows affected

select * from TA natural join TB


TA_1
TB_1


1
1

2
1

3
1

1
2

2
2

3
2

1
3

2
3

3
3