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date caculate in SQL/400?

Posted on 2000-03-15
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I want to add a month to my date field in sql like:
select curdate+ 1 months from ...
In SQL server, I can use DateAdd() function, how to do it in SQL/400?
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Question by:keynes
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by:P_S_Price
ID: 2650036
Extract from AS/400 Manuals which can be found at

http://publib.boulder.ibm.com/pubs/html/as400/online/v4r3eng.htm


2.15.10.1 Date Arithmetic
Dates can be subtracted, incremented, or decremented.


Subtracting Dates: The result of subtracting one date (DATE2) from another (DATE1) is a date duration that specifies the number of years, months, and days between the two dates. The data type of the result is DECIMAL(8,0). If DATE1 is greater than or equal to DATE2, DATE2 is subtracted from DATE1. If DATE1 is less than DATE2, however, DATE1 is subtracted from DATE2, and the sign of the result is made negative. The following procedural description clarifies the steps involved in the operation RESULT = DATE1 - DATE2.

If DAY(DATE2) <= DAY(DATE1) then DAY(RESULT) = DAY(DATE1) - DAY(DATE2).

If DAY(DATE2) > DAY(DATE1) then DAY(RESULT) = N + DAY(DATE1) - DAY(DATE2) where N = the last day of MONTH(DATE2). MONTH(DATE2) is then incremented by 1.

If MONTH(DATE2) <= MONTH(DATE1) then MONTH(RESULT) = MONTH(DATE1) - MONTH(DATE2).

If MONTH(DATE2) > MONTH(DATE1) then MONTH(RESULT) = 12 + MONTH(DATE1) - MONTH(DATE2). YEAR(DATE2) is then incremented by 1.

YEAR(RESULT) = YEAR(DATE1) - YEAR(DATE2).

For example, the result of DATE('3/15/2000') - '12/31/1999' is 215 (or, a duration of 0 years, 2 months, and 15 days).


Incrementing and Decrementing Dates: The result of adding a duration to a date, or of subtracting a duration from a date, is itself a date. (For the purposes of this operation, a month denotes the equivalent of a calendar page. Adding months to a date, then, is like turning the pages of a calendar, starting with the page on which the date appears.) The result must fall between the dates January 1, 0001 and December 31, 9999 inclusive. If a duration of years is added or subtracted, only the year portion of the date is affected. The month is unchanged, as is the day unless the result would be February 29 of a non-leap-year. In this case, the day is changed to 28, and SQLWARN6 in the SQLCA is set to 'W' to indicate the end-of-month adjustment.

Similarly, if a duration of months is added or subtracted, only months and, if necessary, years are affected. The day portion of the date is unchanged unless the result would be invalid (September 31, for example). In this case, the day is set to the last day of the month, and SQLWARN6 in the SQLCA is set to 'W' to indicate the end-of-month adjustment.

Adding or subtracting a duration of days will, of course, affect the day portion of the date, and potentially the month and year. Adding a labeled duration of DAYS will not cause an end-of-month adjustment.

Date durations, whether positive or negative, may also be added to and subtracted from dates. As with labeled durations, the result is a valid date, and a warning indicator is set in the SQLCA whenever an end-of-month adjustment is necessary.

When a positive date duration is added to a date, or a negative date duration is subtracted from a date, the date is incremented by the specified number of years, months, and days, in that order. Thus DATE1 + X, where X is a positive DECIMAL(8,0) number, is equivalent to the expression:

DATE1 + YEAR(X) YEARS + MONTH(X) MONTHS + DAY(X) DAYS

When a positive date duration is subtracted from a date, or a negative date duration is added to a date, the date is decremented by the specified number of days, months, and years, in that order. Thus, DATE1 - X, where X is a positive DECIMAL(8,0) number, is equivalent to the expression:

DATE1 - DAY(X) DAYS - MONTH(X) MONTHS - YEAR(X) YEARS

When adding durations to dates, adding one month to a given date gives the same date one month later unless that date does not exist in the later month. In that case, the date is set to that of the last day of the later month. For example, January 28 plus one month gives February 28; and one month added to January 29, 30, or 31 results in either February 28 or, for a leap year, February 29.

Note: If one or more months is added to a given date and then the same number of months is subtracted from the result, the final date is not necessarily the same as the original date.

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Author Comment

by:keynes
ID: 2652209
I have this book.
But
select curdate+ 100
can not work!!
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Accepted Solution

by:
lly_soft earned 200 total points
ID: 2791069
You can do this

 select current date+(1 months) from ...
 
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Author Comment

by:keynes
ID: 2848863
Answer accepted
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