Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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CHAPTER 12 ■ DATATYPES
9 from dual )
10 /
DAY HOUR MINUTE SECOND
---------- ---------- ---------- ----------
380 10 20 29.878
Additionally, we’ve already seen the NUMTOYMINTERVAL and the NUMTODSINTERVAL for creating
YEAR TO MONTH and DAY TO SECOND intervals. I find these functions to be the easiest way to
create instances of INTERVAL types—over and above the string conversion functions. Rather
than concatenate a bunch of numbers representing the days, hours, minutes, and seconds
representing some interval together, I’d rather add up four calls to NUMTODSINTERVAL to do the
same.
The INTERVAL type can be used to store not just durations, but “times” as well in a way. For
example, if you want to store a specific date and time, you have the DATE or TIMESTAMP types.
But what if you want to store just the time 8:00 am? The INTERVAL type would be handy for that
(the INTERVAL DAY TO SECOND type in particular).
INTERVAL YEAR TO MONTH
The syntax for INTERVAL YEAR TO MONTH is straightforward:
INTERVAL YEAR(n) TO MONTH
where N is an optional number of digits to support for the number of years and varies from
0 to 9, with a default of 2 (to store a number of years from 0 to 99). It allows you to store any
number of years (up to nine digits’ worth, anyway) and months. The function I prefer to use to
create INTERVAL instances of this type is NUMTOYMINTERVAL. For example, to create an interval of
five years and two months, we can use the following:
ops$tkyte@ORA10G> select numtoyminterval(5,'year')+numtoyminterval(2,'month')
2 from dual;
NUMTOYMINTERVAL(5,'YEAR')+NUMTOYMINTERVAL(2,'MONTH')
---------------------------------------------------------------------------
+000000005-02
Or, using a single call and the fact that a year has 12 months, we can use the following:
ops$tkyte@ORA10G> select numtoyminterval(5*12+2,'month')
2 from dual;
NUMTOYMINTERVAL(5*12+2,'MONTH')
---------------------------------------------------------------------------
+000000005-02
Either approach works well. Another function, TO_YMINTERVAL, can be used to convert a
string into a year/month INTERVAL type: