How are dates stored in Oracle?

Question

How are dates stored in Oracle? For example I know most systems use Epoch time to determine what time it is. By calculating how many seconds away from January 1st 1970. Does

Answer 1

How are dates stored in Oracle?

The two data types 12 and 13 are for two different purposes.

• Type 12 - Dates stored in table
• Type 13 - Date returned by internal date functions like SYSDATE/CURRENT_DATE, also when converting a string literal into date using TO_DATE or ANSI Date literal DATE 'YYYY-MM-DD'.

Test cases:

Basic table setup for type 12:

SQL> CREATE TABLE t(col DATE);

Table created.

SQL> INSERT INTO t SELECT SYSDATE FROM dual;

1 row created.

SQL> COMMIT;

Commit complete.

Check the different cases:

SQL> SELECT DUMP(col) FROM t;

DUMP(COL)
--------------------------------------------------------------------------------
Typ=12 Len=7: 120,116,3,17,18,6,55

SQL> SELECT DUMP(SYSDATE) FROM dual;

DUMP(SYSDATE)
--------------------------------------------------------------------------------
Typ=13 Len=8: 224,7,3,17,17,5,54,0

SQL> SELECT DUMP(CURRENT_DATE) FROM dual;

DUMP(CURRENT_DATE)
--------------------------------------------------------------------------------
Typ=13 Len=8: 224,7,3,17,17,14,20,0

SQL> SELECT DUMP(TO_DATE('17-DEC-1980 12:12:12','DD-MON-YYYY HH24:MI:SS'))  FROM dual;

DUMP(TO_DATE('17-DEC-198012:12:12','
------------------------------------
Typ=13 Len=8: 188,7,12,17,12,12,12,0

Using ANSI Date literal, just like TO_DATE:

SQL> SELECT DUMP(DATE '2016-03-17') FROM dual;

DUMP(DATE'2016-03-17')
--------------------------------
Typ=13 Len=8: 224,7,3,17,0,0,0,0

SQL> INSERT INTO t SELECT to_date('17-DEC-1980 12:13:14','DD-MON-YYYY HH24:MI:SS') FROM dual;

1 row created.

SQL> COMMIT;

Commit complete.

SQL> SELECT DUMP(col) FROM t;

DUMP(COL)
--------------------------------------------------------------------------------
Typ=12 Len=7: 120,116,3,17,18,6,55
Typ=12 Len=7: 119,180,12,17,13,14,15

SQL>

As you can see, while storing a date in the table, it uses type 12. The second type 13 is used when converting a string literal into date using date functions or when date returned by internal date functions like SYSDATE/CURRENT_DATE.