Oracle 18c

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CREATE TABLE t
AS
SELECT 1 AS id, 'a' AS cat FROM dual
UNION SELECT 2, 'b' FROM dual
2 rows affected

CREATE TABLE t_ch
AS
SELECT 1 AS id, 1 AS t_id FROM dual
UNION SELECT 2, 3 FROM dual
2 rows affected

SELECT *
FROM t
LEFT JOIN t_ch
  ON t.id = t_ch.t_id
WHERE t.id < 2


ID
CAT
ID
T_ID


1
a
1
1


-- transformed into
select *
from
  T,
  T_CH
where (
  T.ID < 2
  and T.ID = T_CH.T_ID(+)
)


ID
CAT
ID
T_ID


1
a
1
1


SELECT *
FROM t
LEFT JOIN t_ch
  ON t.id = t_ch.t_id
  AND t.id < 2


ID
CAT
ID
T_ID


1
a
1
1

2
b
null
null


-- transformed into
select *
from
  T,
  T_CH
where (
  T.ID = T_CH.T_ID(+)
  and T.ID < 2
)


ID
CAT
ID
T_ID


1
a
1
1


-- CASE 2

select *
from  T,  T_CH
where (T.ID = T_CH.T_ID(+)  AND T_CH.ID = 1)
union all
select *
from  T,  T_CH 
where (T_CH.ID = 1  AND  T.ID = T_CH.T_ID(+))


ID
CAT
ID
T_ID


1
a
1
1

1
a
1
1


select *
from T
  join T_CH
    on T.ID = T_CH.T_ID
where T_CH.ID = 1
union all
select *
from T
  left outer join T_CH
    on T.ID = T_CH.T_ID
where T_CH.ID = 1


QCSJ_C000000000300000
CAT
QCSJ_C000000000300001
T_ID


1
a
1
1

1
a
1
1

ID	CAT	ID	T_ID
1	a	1	1
2	b	null	null