2008-11-24
Among various helpful functions provided by Oracle, Trunc function took my attention today because I had to fix a defect where some one has misunderstood and misused this function.
As the name itself suggests, the trunc function is capable of truncating a value. This function can be used either on a date type value or a numeric value.
Using trunc for numeric values
When it comes to numbers, trunc function can return a number truncated to a certain number of decimal places.
syntax:
trunc( number, [ decimal_places ] )
Example usage:
| trunc(125.815) | would return 125 |
| trunc(125.815, 0) | would return 125 |
| trunc(125.815, 1) | would return 125.8 |
| trunc(125.815, 2) | would return 125.81 |
| trunc(125.815, 3) | would return 125.815 |
| trunc(-125.815, 2) | would return -125.81 |
| trunc(125.815, -1) | would return 120 |
| trunc(125.815, -2) | would return 100 |
| trunc(125.815, -3) | would return 0 |
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Note: The trunc function does not round the values like in round function. It simply truncates the number as instructed.
Using trunc for date values
The trunc function is capable to truncate a date value to a specific unit of measure.
Syntax:
trunc ( date, [ format ] )
Possible values for format parameter:
| Unit | Valid format parameters |
|---|---|
| Year | SYYYY, YYYY, YEAR, SYEAR, YYY, YY, Y |
| ISO Year | IYYY, IY, I |
| Quarter | Q |
| Month | MONTH, MON, MM, RM |
| Week | WW |
| IW | IW |
| W | W |
| Day | DDD, DD, J |
| Start day of the week | DAY, DY, D |
| Hour | HH, HH12, HH24 |
| Minute | MI |
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Example Usage:
| trunc(to_date(’22-AUG-03′), ‘YEAR’) | would return ’01-JAN-03′ |
| trunc(to_date(’22-AUG-03′), ‘Q’) | would return ’01-JUL-03′ |
| trunc(to_date(’22-AUG-03′), ‘MONTH’) | would return ’01-AUG-03′ |
| trunc(to_date(’22-AUG-03′), ‘DDD’) | would return ’22-AUG-03′ |
| trunc(to_date(’22-AUG-03′), ‘DAY’) | would return ’17-AUG-03′ |
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Was this post helpful to you? How can I improve? – Your comment is highly appreciated!
Cassian Menol Razeek
I Learnt Today 
great post, great blog!
you really explained it very well 🙂
I just didn’t got in example ‘DAY’ returns 17-AUG-03? what’s the difference between DAY and DDD
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Hi Alavian,
Thanks for your kind feedback. Appriciate it.
DDD would format the exact date you provided
e.g.
trunc(to_date(’22-AUG-03′), ‘DDD’)
would return ’22-AUG-03′
This is the exact day only formatted the way you specified.
On the other hand, DAY would return the FIRST DAY of that particular week.
e.g.
When you use following command,
trunc(to_date(’22-AUG-03′), ‘DAY’)
Then Oracle would look at the calender to see the week this day (22/08/2003) belongs to and will return the starting day of that week (which is 17th).
So it would return ’17-AUG-03′
I hope this is clear enough.
Wish you great future…
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Hi Menol,
So, trunc(to_date(’22-AUG-03′), ‘DDD’)
and
trunc(to_date(’22-AUG-03′)).
Are they not same?
SELECT TRUNC (TO_DATE (’22-AUG-03′)) WITH_DDD, TRUNC (TO_DATE (’22-AUG-03′), ‘DDD’) WITHOUT_DDD
FROM DUAL;
Thank You,
Abhinav Dixit
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Hi Abhinav,
The results you get may be the same but the process isn’t.
When you don’t specify the formatting string, then the formatter will use current culture settings it can find in the database server. These settings can easily be changed by an admin for different purposes.
If current culture settings in the server are same to what you want then you are fine as long as those culture settings remain same. When someone changes those settings then the result you get will not be the same.
On the other hand, when you specify the format you can rest assured that the output will be exactly what you want regardless of any cultural changes to the server.
Thanks.
Menol
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