An interval expression yields a value of INTERVAL
YEAR
TO
MONTH
or INTERVAL
DAY
TO
SECOND
.
The interval_value_expr
can be the value of an INTERVAL
column or a compound expression that yields an interval value. Datetimes and intervals can be combined according to the rules defined in Table 2-5. The six combinations that yield interval values are valid in an interval expression.
Both leading_field_precision
and fractional_second_precision
can be any integer from 0 to 9. If you omit the leading_field_precision
for either DAY
or YEAR
, then Oracle Database uses the default value of 2. If you omit the fractional_second_precision
for second, then the database uses the default value of 6. If the value returned by a query contains more digits that the default precision, then Oracle Database returns an error. Therefore, it is good practice to specify a precision that you know will be at least as large as any value returned by the query.
For example, the following statement subtracts the value of the order_date
column in the sample table orders
(a datetime value) from the system timestamp (another datetime value) to yield an interval value expression. Because we do not know how many days ago the oldest order was placed, we specify the maximum value of 9 for the DAY
lading field precision:
SELECT (SYSTIMESTAMP - order_date) DAY(9) TO SECOND FROM orders WHERE order_id = 2458;