TO_DATE function in Oracle is the most useful as well as ‘annoying’ function.

TO_DATE function converts string into date data types.

Eg :-

select to_date(‘2016/11/13′,’yyyy/mm/dd’) from dual;

returns  2016/11/13

Note that Oracle converts string ‘2016/11/13’into Date ‘2016/11/13’. Now this value can be inserted into a table having a column date data type.

Note :- Before doing any testing on date columns make sure the default date format settings

For example in my sqldeveloper tool, go to Tools–> Preferences –> Database –> NLS

Below sql should have returned 2016/11/13, but shows 13-NOV-16 which is in sqldeveloper nls date format. This is the most common mistake developers make.

Alternatively you can use below sql also to change the date format.

alter session set nls_date_format = ‘dd-mon-yyyy’;

The above SQL can be used from SQLPLUS also.

If you do not want to change the nls settings, you can use TO_CHAR function also in required format, see below example.

select to_char(to_date(‘2016/11/13′,’yyyy/mm/dd’),’yyyy/mm/dd’) from dual;

(TO_CHAR and TO_DATE)

Important :-  Oracle stores date data type with time.

Below are the most used formats with TO_DATE

Format	Description	Example	Value
AD	AD or BC	to_char(to_date(‘2016/11/13 AD’,’yyyy/mm/dd AD’),’AD’)	AD
BC	AD or BC	to_char(to_date(‘2016/11/13 BC’,’yyyy/mm/dd AD’),’AD’)	BC
D	Day of week (1 7)	to_char(to_date(‘2016/11/13′,’yyyy/mm/dd’),’D’)	1
DAY	Name of day	to_char(to_date(‘2016/11/13′,’yyyy/mm/dd’),’DAY’)	SUNDAY
DD	Day of month (1 31)	to_char(to_date(‘2016/11/13′,’yyyy/mm/dd’),’DD’)	13
DDD	Day of year (1 366)	to_char(to_date(‘2016/11/13′,’yyyy/mm/dd’),’DDD’)	318
DY	Abbr name of day	to_char(to_date(‘2016/11/13′,’yyyy/mm/dd’),’DY’)	SUN
HH	Hour of day (1 12)	to_char(to_date(‘2016/11/13 01:12:35′,’yyyy/mm/dd hh:mi:ss’),’HH’)	‘01’
HH12	Hour of day (1 12)	to_char(to_date(‘2016/11/13 04:12:35 PM’,’yyyy/mm/dd hh:mi:ss PM’),’HH12′)	‘04’
HH24	Hour of day (0 23)	to_char(to_date(‘2016/11/13 04:12:35 PM’,’yyyy/mm/dd hh:mi:ss PM’),’HH24′)	16
IW	Week of year	to_char(to_date(‘2016/11/13′,’yyyy/mm/dd’),’IW’)	45
J	Julian day	to_char(to_date(‘2016/11/13′,’yyyy/mm/dd’),’J’)	2457706
MI	Minute (0 59)	to_char(to_date(‘2016/11/13 01:12:35′,’yyyy/mm/dd hh:mi:ss’),’MI’)	12
MM	Month (01 etc)	to_char(to_date(‘2016/11/13 01:12:35′,’yyyy/mm/dd hh:mi:ss’),’MM’)	11
MON	Abbr month	to_char(to_date(‘2016/11/13 01:12:35′,’yyyy/mm/dd hh:mi:ss’),’MON’)	NOV
MONTH	Name of month	to_char(to_date(‘2016/11/13 01:12:35′,’yyyy/mm/dd hh:mi:ss’),’MONTH’)	NOVEMBER
AM	AM or PM	to_char(to_date(‘2016/11/13 01:12:35 AM’,’yyyy/mm/dd hh:mi:ss AM’),’AM’)	AM
PM	AM or PM	to_char(to_date(‘2016/11/13 01:12:35 PM’,’yyyy/mm/dd hh:mi:ss AM’),’AM’)	PM
Q	Quarter of year	to_char(to_date(‘2016/11/13 01:12:35 AM’,’yyyy/mm/dd hh:mi:ss AM’),’Q’)	4
RRRR	Round year	to_char(to_date(‘2016/11/13 01:12:35 AM’,’yyyy/mm/dd hh:mi:ss AM’),’RRRR’)	2016
SS	Second (0 59)	to_char(to_date(‘2016/11/13 01:12:35 AM’,’yyyy/mm/dd hh:mi:ss AM’),’SS’)	35
WW	Week of year (1 53)	to_char(to_date(‘2016/11/13 01:12:35 AM’,’yyyy/mm/dd hh:mi:ss AM’),’WW’)	46
W	Week of month (1 5)	to_char(to_date(‘2016/11/13 01:12:35 AM’,’yyyy/mm/dd hh:mi:ss AM’),’W’)	2
YYYY	Last 4 digit(s) of year	to_char(to_date(‘2016/11/13 01:12:35 AM’,’yyyy/mm/dd hh:mi:ss AM’),’YYYY’)	2016
YY	Last 2 digit(s) of year	to_char(to_date(‘2016/11/13 01:12:35 AM’,’yyyy/mm/dd hh:mi:ss AM’),’YY’)	‘16’

Always check below before you start using TO_DATE function

1. NLS_DATE_FORMAT ( SELECT sys_context (‘userenv’,’NLS_DATE_FORMAT’) FROM DUAL )

or

2. use TO_CHAR for formating

Also read TO_CHAR Function