Diferenca entre duas datas:
select to_char( created, 'dd-mon-yyyy hh24:mi:ss' ),
trunc( sysdate-created ) "Dy",
trunc( mod( (sysdate-created)*24, 24 ) ) "Hr",
trunc( mod( (sysdate-created)*24*60, 60 ) ) "Mi",
trunc( mod( (sysdate-created)*24*60*60, 60 ) ) "Sec",
to_char( sysdate, 'dd-mon-yyyy hh24:mi:ss' ),
sysdate-created "Tdy",
(sysdate-created)*24 "Thr",
(sysdate-created)*24*60 "Tmi",
(sysdate-created)*24*60*60 "Tsec"
from all_users
where rownum < 50
/
Adapte para sua necessidade. Referencia: http://asktom.oracle.com/tkyte/Misc/DateDiff.html
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