Oracle 11g Release 2

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CREATE TABLE XXBCT_BIO_OTL_ENTRIES_SUMMARY (
  EMPLOYEE_NUMBER, ATTENDANCE_DT, SIGN_IN_TIME, SIGN_OUT_TIME
)
AS
SELECT '112319',
       DATE '2019-01-04',
       TO_CHAR( TIMESTAMP '2019-01-04 00:00:00', 'HH24:MI' ),
       TO_CHAR( TIMESTAMP '2019-01-04 08:13:00', 'HH24:MI' )
FROM   DUAL
1 rows affected

SELECT * FROM XXBCT_BIO_OTL_ENTRIES_SUMMARY


EMPLOYEE_NUMBER
ATTENDANCE_DT
SIGN_IN_TIME
SIGN_OUT_TIME


112319
04-JAN-19
00:00
08:13


SELECT round(
         24 * (to_date(SIGN_OUT_TIME,'hh24:mi') - to_date(SIGN_IN_TIME,'hh24:mi')),
         2
       ) diff_hours
FROM   XXBCT_BIO_OTL_ENTRIES_SUMMARY
WHERE  EMPLOYEE_NUMBER = '112319'
AND    attendance_dt   = DATE '2019-01-04';


DIFF_HOURS


8.22


SELECT ROUND( diff_hours, 2 ) AS diff_hours,
       TRUNC( diff_hours ) + MOD( diff_hours, 1 ) * 0.60 AS diff_hours_hhmi
FROM   (
  SELECT 24 * (to_date(SIGN_OUT_TIME,'hh24:mi') - to_date(SIGN_IN_TIME,'hh24:mi'))
           AS diff_hours
  FROM   XXBCT_BIO_OTL_ENTRIES_SUMMARY
  WHERE  EMPLOYEE_NUMBER = '112319'
  AND    attendance_dt   = DATE '2019-01-04'
);


DIFF_HOURS
DIFF_HOURS_HHMI


8.22
8.13


SELECT TO_TIMESTAMP(SIGN_OUT_TIME,'hh24:mi') - TO_TIMESTAMP(SIGN_IN_TIME,'hh24:mi') AS diff_hours_interval,
       SUBSTR(TO_TIMESTAMP(SIGN_OUT_TIME,'hh24:mi') - TO_TIMESTAMP(SIGN_IN_TIME,'hh24:mi'), 12, 5 ) AS diff_hours_interval_string
FROM   XXBCT_BIO_OTL_ENTRIES_SUMMARY
WHERE  EMPLOYEE_NUMBER = '112319'
AND    attendance_dt   = DATE '2019-01-04';


DIFF_HOURS_INTERVAL
DIFF_HOURS_INTERVAL_STRING


+000000000 08:13:00.000000000
08:13