Chapter 03Using SingleRow Functions to Customize Output(03)

Working with Dates

• The Oracle database stores dates in an internal numeric format:century,year,month,day,hours,minutes,and seconds.
• The default date display format is DD-MON-RR.
  • -Enables you to store 21st-century dates in the 20th century by specifying only the last two digits of the year.
  • -Enables you to store 20th-century dates in the 21st century in the same way.

SQL> SELECT last_name,hire_date FROM employees WHERE hire_date < '01-FEB-03';

LAST_NAME                 HIRE_DATE
------------------------- ---------
Mavris                    07-JUN-02
Baer                      07-JUN-02
Higgins                   07-JUN-02
Gietz                     07-JUN-02
De Haan                   13-JAN-01
Greenberg                 17-AUG-02
Faviet                    16-AUG-02
Raphaely                  07-DEC-02

8 rows selected.

RR Date Format

Current Year	Specified Date	RR Format	YY Format
1995	27-OCT-95	1995	1995
1995	27-OCT-17	2017	1917
2001	27-OCT-17	2017	2017
2001	27-OCT-95	1995	2095

		If the specified two-digit year is:
		0-49	50-99
If two digits of the current year are:	0-49	The return date is in the current centry	The return date is in the century before the current one.
	50-99	The return date is in the century after the current one	The return date is in the current century

 

Using the SYSDATE Function

SYSDATE is a function that returns:

• Date
• Time

SQL> SELECT TO_CHAR(sysdate,'YYYY-MM-DD HH24:MI:SS') CURRENTDATE FROM dual;

CURRENTDATE
-------------------
2013-04-12 13:05:31

Arithmetic With Dates

• Add or subtract a number to or from a date for a resultant date value.
• Subtract two dates to find the number of days between those dates.
• Add hours to a date by dividing the number of hours by 24. 

Using Arithmetic Operators with Dates

SQL> SELECT last_name,(SYSDATE-hire_date)/7 AS WEEKS FROM employees WHERE department_id = 90;

LAST_NAME                      WEEKS
------------------------- ----------
King                      512.508074
Kochhar                   394.365217
De Haan                   638.936645

Date-Mainpulation Functions

Function	Result
MONTHS_BETWEEN	Number of months between two dates
ADD_MONTHS	Add calendar months to date
NEXT_DAY	Next day of the date specified
LAST_DAY	Last day of the month
ROUND	Round date
TRUNC	Truncate date

Using Date Functions And Using ROUND and TRUNC Functions with Dates.

SQL> SELECT MONTHS_BETWEEN('01-SEP-95','11-JAN-94') FROM DUAL;

MONTHS_BETWEEN('01-SEP-95','11-JAN-94')
---------------------------------------
                             19.6774194

SQL> SELECT ADD_MONTHS('31-JAN-96',1) FROM DUAL;

ADD_MONTH
---------
29-FEB-96

SQL> SELECT NEXT_DAY('01-SEP-95','FRIDAY') FROM DUAL;

NEXT_DAY(
---------
08-SEP-95

SQL> SELECT LAST_DAY('01-FEB-95') FROM DUAL;

LAST_DAY(
---------
28-FEB-95

SQL>

SQL> SELECT SYSDATE FROM DUAL;

SYSDATE
---------
12-APR-13

SQL> SELECT ROUND(SYSDATE,'MONTH') FROM DUAL;

ROUND(SYS
---------
01-APR-13

SQL> SELECT ROUND(SYSDATE,'YEAR') FROM DUAL;

ROUND(SYS
---------
01-JAN-13

SQL> SELECT TRUNC(SYSDATE,'MONTH') FROM DUAL;

TRUNC(SYS
---------
01-APR-13

SQL> SELECT TRUNC(SYSDATE,'YEAR') FROM DUAL;

TRUNC(SYS
---------
01-JAN-13

SQL>

Summary

In this lesson,you should have learned how to:

• Perform calulations on data using functions.
• Modify individual data items using funcions.