Oracle 11g Release 2

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create table test (
    id number primary key, 
    not_clob varchar2(255),
    this_is_clob clob
);

BEGIN
insert into test values (1, 'test1', to_clob('clob1'));
insert into test values (2, 'test2', to_clob('clob2'));
END;
/
1 rows affected

select id, lag( TO_CHAR(this_is_clob)) over (order by id) from test;


ID
LAG(TO_CHAR(THIS_IS_CLOB))OVER(ORDERBYID)


1
null

2
clob1


SELECT a.id,
       b.this_is_clob AS lagging
FROM test a
LEFT JOIN test b ON b.id < a.id;


ID
LAGGING


1
null

2
clob1