Tuesday, November 03, 2015

2 level left outer join

Here is Oracle outer join behavior observation.
We get same results between Oracle notation (+), and ANSI join syntax (LEFT OUTER JOIN)

Oracle 12.1.0.2.0

drop table t1 purge;
drop table t2 purge;
drop table t3 purge;


create table t1 (id number);
create table t2 (id number);
create table t3 (id number);


insert into t1(id) select rownum from dual connect by level <= 3;
insert into t2(id) select rownum from dual connect by level <= 2;
insert into t3(id) select rownum from dual connect by level <= 1;
commit;


select t1.id t1_id, t2.id t2_id, t3.id t3_id
from t3,t2,t1
where t1.id = t2.id(+)
and t2.id = t3.id(+)
order by t1.id;


  T1_ID   T2_ID    T3_ID
------- ------- --------
      1       1        1
      2       2
      3


drop table t1 purge;
drop table t2 purge;
drop table t3 purge;


create table t1 (id number);
create table t2 (id number, t1_id number);
create table t3 (id number, t2_id number);


insert into t1(id) select rownum from dual connect by level <= 3;
insert into t2(id, t1_id) select rownum, rownum from dual connect by level <= 2;
insert into t3(id, t2_id) select rownum, rownum from dual connect by level <= 1;

commit;

select t1.id, t2.id t2_id, t2.t1_id, t3.id t3_id, t3.t2_id
from t3,t2,t1
where t1.id = t2.t1_id(+)
and t2.id = t3.t2_id(+)
order by t1.id;


  ID  T2_ID  T1_ID  T3_ID  T2_ID
---- ------ ------ ------ ------
   1      1      1      1      1
   2      2      2
   3


Your homework is to write ANSI join syntax (LEFT OUTER JOIN) SQL, to get same result.   ^_^
Post a Comment