Mastering Oracle SQL Date Arithmetic

Topics Introduction

Date Arithmetic is the calculations based on date. Doing Date calculations is a night mare many times for a developer, especially in Oracle many developer felt this. But many of us never knew simple tricks and the new features (like INTERVAL introduced in Oracle 9). If you know and understand various date functions thoroughly, you may not feel this as a pain.

For a better understanding, let me put the various possible operations as topics here.

• Add days, months, years to Date
• Subtract days, months, years from date
• Difference between dates
• Comparing Dates
• Some Special Oracle date functions
• Interval and timestamp data types
• Type Conversion

If you explore these simple steps thoroughly, you may feel your self as an expert of date arithmetic in Oracle. After reading this ready the topic on Oracle Analytic Functions which could make you an expert.

Add days, months, years to Date

Adding to a date is as simple as adding numbers. Yes you can use ‘+' operator straight away. For example SYSDATE+7 gives you 7 days or a week after SYSDATE. So, if you want to add one month you will easily conclude SYSDATE + 30. Good. But this is not correct.

What would be the result of SYSDATE + 30 if the number of days in current month is 31? it would give one day lesser than what we expect. If SYSDATE is 01-SEP-2008, the result will give 01-OCT-2008 and which is seamlessly wrong. This is where Oracles ADD_MONTHS date function plays the role. ADD_MONTHS(SYSDATE, 1) will give the date after a month. The second parameter is number of months and here it says add 1 month to SYSDATE. No need to worry whether it is January or February or August etc.

Ok! I want to take you one step ahead, how to calculate the day after one year. I would give you a clue. And the clue is - 'A year has only 12 months'. Yes you are correct ADD_MONTHS(SYSDATE, 12) will give day after 1 year.

Did you thought ADD_YEARS(SYSDATE, 1)? Ha Ha! Good thinking! But Oracle has not yet provided such function. You can create a custom function using above calculation.

Example

`DECLARE`
`  today DATE :=sysdate;`
`  future DATE;`
`BEGIN`
`  future := today + 45;`
`  dbms_output.put_line('Today is:' || today);`
`  dbms_output.put_line('Day after 45 days is:' || future);`
`  future := ADD_MONTHS(today, 2);`
`  dbms_output.put_line('Day after 2 months is:' || future);`
`  future := ADD_MONTHS(today, 12);`
`  dbms_output.put_line('Day after 1 year is:' || future);`
`END;`
`/`
`Output will be `
`Today is:01-SEP-08`
`Day after 45 days is:16-OCT-08`
`Day after 2 months is:01-NOV-08`
`Day after 1 year is:01-SEP-09`

Subtract days, months, years from a date in Oracle

Yes you will be picking up fast if you say just replace negative sign in place of the + operator. But what happens to ADD_MONTHS? Is there is a function SUBTRACT_MONTHS? Ahhhh! But not that. Just put the number of months to add in negative sign.

Example

`DECLARE`
`  today DATE :=sysdate;`
`  past DATE;`
`BEGIN`
`  past := today - 45;`
`  dbms_output.put_line('Today is:' || today);`
`  dbms_output.put_line('Day before 45 days is:' || past);`
`  past := ADD_MONTHS(today, -2);`
`  dbms_output.put_line('Day before 2 months is:' || past);`
`  past := ADD_MONTHS(today, -12);`
`  dbms_output.put_line('Day before 1 year is:' || past);`
`END;`
`/`
`Output will be`
`Today is:02-SEP-08`
`Day before 45 days is:19-JUL-08`
`Day before 2 months is:02-JUL-08`
`Day before 1 year is:02-SEP-07`

Find Difference between dates in Oracle

Still we can use very simple of operations by using - operator which gives number of days between two dates. Refer below example.

`DECLARE`
`   d1 DATE := '01-Aug-2008';`
`   today DATE := TRUNC(SYSDATE);`
`BEGIN`
`   dbms_output.put_line('No of days between two dates:' || (today-d1) );`
`END;`

/

`Output will be`
`No of days between two dates:31`

Looks very simple right? Errrr! But what is that TRUNC? This function cuts the time part of sysdate. Just place SYSDATE in place of TRUNC(SYSDATE), you will see the same output as fraction. The fraction reflects the time difference. So, Just to ignore that I have put this.

Now, you may think how to interpret into month or year? Here is the role of the Oracle date function MONTHS_BETWEEN comes.

MONTHS_BETWEEN(date1, date2) gives the number of months between two dates. Say I have joined in a company on '01-Jul-2007' and still working in that company. Below code will give my experience in months.

`DECLARE`
`  joined_on DATE := '01-JUL-2007';`
`  today DATE := TRUNC(sysdate, 'mm');`
`BEGIN`
`  dbms_output.put_line('I have bee working here for ' || `
`                     MONTHS_BETWEEN(today, joined_on) || ‘ months' );`
`END;`
`/`
`Output will be`
`I have bee working here for 14 months`

Interesting? I think now you are more confident with date arithmetic than you are earlier.

Comparing Dates

This is not as complex as previous ones. This similar to the fashion you compare other data (numeric/character). Ye you can use the operators <, >, =, <> operators.

Below example illustrates simply to you straight away. The example analyzes between three brothers John, Peter and David taking their date of birth.

`DECLARE`
`   johns_dob DATE := '01-JUL-1960';`
`   peters_dob DATE := '01-JUL-1970';`
`   davids_dob DATE := '01-JUL-1960';`
`BEGIN`
`   IF johns_dob <> peters_dob THEN`
`   --both born on different dates`
`      IF johns_dob < peters_dob THEN`
`         dbms_output.put_line('John is younger to Peter!');`
`      ELSE`
`         dbms_output.put_line('John is elder to Peter!');`
`      END IF;`
`   elsif johns_dob = peters_dob THEN`
`      dbms_output.put_line('John and Peter are Twins!');`
`   ELSE`
`      dbms_output.put_line('This is impossible any way!! ');`
`      --Find out why this is never possible if you give values!`
`      --A logical test for you! Solve & Give your comments --`
`   END IF;`
`   IF johns_dob <> davids_dob THEN`
`      --both born on different dates`
`      IF johns_dob < davids_dob THEN`
`         dbms_output.put_line('John is younger to David!');`
`      ELSE`
`         dbms_output.put_line('John is elder to David!');`
`      END IF;`
`   elsif johns_dob = davids_dob THEN`
`      dbms_output.put_line('John and david are Twins!');`
`   END IF;`
`END;`
`/`
`Output should be:`
`John is younger to Peter!`
`John and david are Twins!`

Some special date functions

Yes there are more features in Oracle to perform date arithmetic. I list them here for your reference.

SYSDATE returns the current date and time of your operating system (the place where your oracle server is running). This is a pseudo column.

SYSTIMESTAMP similar to SYSDATE but it includes fractional seconds and time zone.

TRUNC(date) trims off the time portion of given date.

TRUNC(date, ‘mm') returns the first day of month for given date.

LAST_DAY(date) returns the last day of month for given date.

EXTRACT extracts and returns the specified value from a date or time. You can pull the day, month, year, hour and more from a date using below syntax.

`EXTRACT ( `
`{ YEAR | MONTH | DAY | HOUR | MINUTE | SECOND } `
`| { TIMEZONE_HOUR | TIMEZONE_MINUTE } `
`| { TIMEZONE_REGION | TIMEZONE_ABBR } `
`FROM { date_value | interval_value } )`

But important thing is you can pull only a day, month or year from a date value. For pulling hours, minutes, time zone you need to use interval value using which you can't pull day/month/year.

Example

`SELECT EXTRACT(DAY FROM SYSDATE) FROM DUAL;`
`EXTRACT(DAYFROMSYSDATE) `
`----------------------- `
`2 `
`SELECT EXTRACT(MONTH FROM SYSDATE) FROM DUAL;`
`EXTRACT(MONTHFROMSYSDATE) `
`------------------------- `
`9 `
`SELECT EXTRACT(YEAR FROM SYSDATE) FROM DUAL;`
`EXTRACT(YEARFROMSYSDATE) `
`------------------------ `
```2008

```

Type Conversion of Oracle Date Data Type

Oracle provides many functions for date and time conversions. Apart from that, TO_DATE and TO_CHAR are very familiar functions.

• TO_DATE converts character data into a DATE.
• TO_CHAR converts DATE into character data.

Example

• TO_DATE(‘25/01/2008', ‘dd/mm/yyyy') - Returns the value '25-JAN-08' of type date.
• TO_CHAR(SYSDATE, ‘MON') - Returns the abbreviated month name

There are so many other functions available for conversion of intervals. I have listed them below.

• NUMTODSINTERVAL converts a NUMBER or expression into a DAY TO SECOND interval.
• NUMTOYMINTERVAL, converts a NUMBER or expression into a YEAR TO MONTH interval.
• TO_DSINTERVAL converts string to DAY TO SECOND interval.
• TO_YMINTERVAL converts a character string to YEAR TO MONTH type
• TO_TIMESTAMP converts to TIMESTAMP
• TO_TIMESTAMP_TZ converts character data to TIMESTAMP WITH TIME ZONE

I leave the examples for conversion as an exercise for you with the hope that you have got enough confidence now.

Read my article on Oracle Exceptions to write efficient code with error handling features.

Click below example to enlarge.

More by this Author

hot dorkage 8 years ago from Oregon, USA

Great hub it's nice to compare the difference between Oracle SQL and mySQL. I wonder how many hubbers are into raw Oracle SQL though.

selvirajan 8 years ago from India Author

I liked your hubs on oracle. Thats really interesting. Especially the series of articles on "SQL Sins". Its really a honour to get appreciating comments from a expert here.

rajesh 8 years ago

sherlynavia 8 years ago from United States

Nice hub!

sherlynavia 8 years ago from United States

Nice hub!

Akshay 8 years ago

Too Good

Bharath 8 years ago

I learnt many new things from this website. gr8 site.

New Dating Sites 7 years ago

Great page lol @ Bharath

Ankur  7 years ago

How to calculate no. of days,months and years between two dates. Dates Like that first date is '01-Jan-2007' and second date is 15-july-2009.

Niels Jessen 7 years ago

Ankur:

Calculate months between dates; months_between(date1,date2) ==> example ==>

months_between(trunc(sysdate + 394,'mm'),trunc(sysdate,'mm'))

Calculate years between dates: months_between(date1,date2)/12 ==> example

select months_between(trunc(sysdate + 394,'mm'),trunc(sysdate,'mm'))/12 from dual;

jagath 7 years ago

oracle arithmetic does not work as you mentioned "What would be the result of SYSDATE + 30 if the number of days in current month is 31? it would give one day lesser than what we expect. If SYSDATE is 01-SEP-2008, the result will give 31-SEP-2008" , you have got it wrong

gramsmith 6 years ago

Thanks for this great article.Keep on writing.............

Alberto 6 years ago

DECLARE @TODAY DATETIME

SET @TODAY = GETDATE()

DECLARE @BEFORE DATETIME

SET @BEFORE = GETDATE()-30

SELECT COUNT(INTERACTIONID)

FROM INTERACTIONS

WHERE CAST(CONVERT(DATETIME, '1970-01-01 00:00:00.000') + DATEADD(HH,-7,(STARTDATE/86400.0))

BETWEEN @BEFORE AND @TODAY

AND ORIGINATOR = '\$ANI'

Alberto 6 years ago

I'm sorry, the actual code is,

DECLARE @today DATETIME

SET @today = getdate()

DECLARE @BEFORE DATETIME

SET @BEFORE = getdate()-30

SELECT COUNT(InterActionID) as total

FROM INTERACTIONS

WHERE CAST(CONVERT(DATETIME, '1970-01-01 00:00:00.000') + dateadd(hh,-7,(STARTDATE/86400.0)) AS DATETIME)

between @before AND @today

and Originator = '1234567891'

araj 6 years ago

ITs toooo gud and very helpful.....

kpc 6 years ago

can u tell the answer to comparing dates question

Sara 4 years ago

nicely explained the simple and important topic; I used to face a lot many problems with date calculations including date format specification of different countries; ur hub is informative. thanks

Cyrille MODIANO 2 years ago from Montreal

very well explained, thank you for sharing this !

monsAvalsesem 15 months ago

Thanks for introducing a little ratioanltiy into this debate.

selvirajan 6 months ago from India Author

Back here after few years. Glad that still this helped many people.

Thanks to all the viewers who made this interactive while i am away. Would try to catch up slowly and regularly.