Oracle 11g Release 2

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CREATE TABLE T1(ID varchar(10), COL1 VARCHAR(10), COL2 varchar(10));
INSERT INTO T1
SELECT 't1' ID,    'data1' COL1,     'data2' COL2 FROM DUAL
UNION ALL
SELECT 't2',   'data3',     'data4' FROM DUAL
2 rows affected

CREATE TABLE T2(idOfTable1 varchar(10), COL3 VARCHAR(10), col4 varchar(10));
insert into T2
SELECT 't1' idOfTable1,           'data5' COL3,       'data6' COL4 FROM DUAL
UNION ALL
SELECT 't1',           'data7',      'data8' FROM DUAL
UNION ALL
SELECT 't1',           'data9',      'data10' FROM DUAL
UNION ALL
SELECT 't2',         'data11',     'data12' FROM DUAL
4 rows affected

SELECT CASE WHEN LAG(T1.ID) OVER(PARTITION BY T1.ID ORDER BY T2.COL3) = T1.ID 
       THEN NULL
       ELSE T1.ID END AS ID,
       CASE WHEN LAG(T1.ID) OVER(PARTITION BY T1.ID ORDER BY T2.COL3) = T1.ID
       THEN NULL
       ELSE T1.COL1 END AS COL1,
       CASE WHEN LAG(T1.ID) OVER(PARTITION BY T1.ID ORDER BY T2.COL3) = T1.ID
       THEN NULL
       ELSE T1.COL2 END AS COL2,
       T2.COL3,
       T2.COL4
FROM T1
JOIN T2 ON T1.id = T2.idOfTable1
ORDER BY T1.ID, T2.COL3


ID
COL1
COL2
COL3
COL4


t1
data1
data2
data5
data6

null
null
null
data7
data8

null
null
null
data9
data10

t2
data3
data4
data11
data12

ID	COL1	COL2	COL3	COL4
t1	data1	data2	data5	data6
null	null	null	data7	data8
null	null	null	data9	data10
t2	data3	data4	data11	data12