MySQL Cookbook

Calculating Intervals Between Times

Problem

You want to know the amount of time elapsed between two times.

Solution

Convert the times to seconds with TIME_TO_SEC( ) and take the difference. For a difference represented as a time, convert the result back the other way using SEC_TO_TIME( ).

Discussion

Calculating intervals between times is similar to adding times together, except that you compute a difference rather than a sum. For example, to calculate intervals in seconds between pairs of t1 and t2 values, convert the values in the time_val table to seconds using TIME_TO_SEC( ), then take the difference. To express the resulting difference as a TIME value, pass it to SEC_TO_TIME( ). The following query shows intervals both ways:

mysql> SELECT t1, t2,
    -> TIME_TO_SEC(t2) - TIME_TO_SEC(t1) AS 'interval in seconds',
    -> SEC_TO_TIME(TIME_TO_SEC(t2) - TIME_TO_SEC(t1)) AS 'interval as TIME'
    -> FROM time_val;
+----------+----------+---------------------+------------------+
| t1       | t2       | interval in seconds | interval as TIME |
+----------+----------+---------------------+------------------+
| 15:00:00 | 15:00:00 |                   0 | 00:00:00         |
| 05:01:30 | 02:30:20 |               -9070 | -02:31:10        |
| 12:30:20 | 17:30:45 |               18025 | 05:00:25         |
+----------+----------+---------------------+------------------+

Note that intervals may be negative, as is the case when t1 occurs later than t2.