5.15.1 Problem
You want to know the amount of time elapsed between two times.
5.15.2 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( ).
5.15.3 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.
Using the mysql Client Program
Writing MySQL-Based Programs
Record Selection Techniques
Working with Strings
Working with Dates and Times
Sorting Query Results
Generating Summaries
Modifying Tables with ALTER TABLE
Obtaining and Using Metadata
Importing and Exporting Data
Generating and Using Sequences
Using Multiple Tables
Statistical Techniques
Handling Duplicates
Performing Transactions
Introduction to MySQL on the Web
Incorporating Query Resultsinto Web Pages
Processing Web Input with MySQL
Using MySQL-Based Web Session Management
Appendix A. Obtaining MySQL Software
Appendix B. JSP and Tomcat Primer
Appendix C. References