MySQL Cookbook

Calculating Intervals Between Dates

Problem

You want to know how long it is between dates.

Solution

Convert both dates to basic units and take the difference between the resulting values.

Discussion

The general procedure for calculating an interval between dates is to convert both dates to a common unit in relation to a given reference point, then take the difference. The range of values you’re working with determines which conversions are available. DATE, DATETIME, or TIMESTAMP values dating back to 1970-01-01 00:00:00 GMT—the date of the Unix epoch—can be converted to seconds elapsed since the epoch. If both dates lie within that range, you can calculate intervals to an accuracy of one second. Older dates from the beginning of the Gregorian calendar (1582) on can be converted to day values and used to compute intervals in days. Dates that begin earlier than either of these reference points present more of a problem. In such cases, you may find that your programming language offers computations that are not available or are difficult to perform in SQL. If so, consider processing date values directly from within your API language. (For example, the Date::Calc and Date::Manip modules are available from the CPAN for use within Perl scripts.)

To calculate an interval in days between date or date-and-time values, convert them to days using TO_DAYS( ), then take the difference:

mysql> SELECT TO_DAYS('1884-01-01') - TO_DAYS('1883-06-05') AS days; +------+ | days | +------+ | 210 | +------+ ...