
String Expressions  Expressions  Rounding Numbers in SQL 
You can add or substract an integer number (as an interval) from values of DATE, TIME and TIMESTAMP types. You can also count the numerical difference of two values of the same type and get an integer value.
The interval specifies the number of days for DATE type, number of thousandths of seconds for TIME type and number of seconds for TIMESTAMP type (e.g. You can have an interval as a result of two TIME type values substraction. To add this to a TIMESTAMP type value you must divide it by one thousand first).
If the first operand in a expression is a literal of TIME or TIMESTAMP types, you must specify at least one blank space before the + or  operator, so the addition or subtraction is not mistaken as the time zone entry. The first plus in the following example is a time zone specification, the second is the operator for "adding a thousandth of a second".
SET tm = 12:24:00+02 + 30*1000;
602SQL Variances
Example:
Select invoices from the last ten days using the CURRENT_DATE function to get the date.
SELECT number,date1 FROM Invoices WHERE date1 BETWEEN CURRENT_DATE10 AND CURRENT_DATE
String Expressions  Expressions  Rounding Numbers in SQL 