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Relational operators
212
• Addition and subtraction, from left to right
Date arithmetic expressions
Date arithmetic expressions compute the difference between date-time expressions in terms of
days or milliseconds. SQL supports these forms of date arithmetic:
• Addition and subtraction of integers to and from date-time expressions
• Subtraction of one date-time expression from another
Syntax
date_time_expr { + | - } int_expr
| date_time_expr - date_time_expr
date_time_expr
int_expr
Returns a value of type DATE or TIME or TIMESTAMP. A single date-time expression cannot
mix data types, however. All elements of the expression must be the same data type.
Date-time expressions can contain date-time literals, but they must be converted to DATE
or TIME using the CAST, CONVERT, or TO_DATE functions.
Returns an integer value. SQL interprets the integer differently depending on the data type
of the date-time expression:
• For DATE expressions, integers represent days
• For TIME expressions, integers represent milliseconds
• For TIMESTAMP expressions, integers represent milliseconds
Examples The following example manipulates DATE values using date arithmetic. SQL interprets integers
as days and returns date differences in units of days:
SELECT C1, C2, C1-C2 FROM DTEST
c1 c2 c1-c2
---------------------------------------
1956-05-07 1952-09-29 1316
select sysdate,
sysdate - 3 ,
sysdate - cast ('9/29/52' as date)
from dtest;
sysdate sysdate-3 sysdate-convert(date,9/29/52)
----------------------------------------------------------
1995-03-24 1995-03-21 15516
The following example manipulates TIME values using date arithmetic. SQL interprets integers
as milliseconds and returns time differences in milliseconds: