If you pass TIME_TO_SEC( ) a date-and-time value, it extracts the time part and discards the date.

      
mysql>
mysql>
mysql> CREATE TABLE datetime_val
    -> (
    ->  dt      DATETIME
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>
mysql> INSERT INTO datetime_val (dt) VALUES('1970-01-01 00:00:00');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO datetime_val (dt) VALUES('1987-03-05 12:30:15');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO datetime_val (dt) VALUES('1999-12-31 09:00:00');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO datetime_val (dt) VALUES('2000-06-04 15:45:30');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> SELECT * FROM datetime_val;
+---------------------+
| dt                  |
+---------------------+
| 1970-01-01 00:00:00 |
| 1987-03-05 12:30:15 |
| 1999-12-31 09:00:00 |
| 2000-06-04 15:45:30 |
+---------------------+
4 rows in set (0.00 sec)

mysql>
mysql>
mysql> SELECT dt,
    -> TIME_TO_SEC(dt) AS 'time part in seconds',
    -> SEC_TO_TIME(TIME_TO_SEC(dt)) AS 'time part as TIME'
    -> FROM datetime_val;
+---------------------+----------------------+-------------------+
| dt                  | time part in seconds | time part as TIME |
+---------------------+----------------------+-------------------+
| 1970-01-01 00:00:00 |                    0 | 00:00:00          |
| 1987-03-05 12:30:15 |                45015 | 12:30:15          |
| 1999-12-31 09:00:00 |                32400 | 09:00:00          |
| 2000-06-04 15:45:30 |                56730 | 15:45:30          |
+---------------------+----------------------+-------------------+
4 rows in set (0.00 sec)

mysql>
mysql> drop table datetime_val;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>
mysql>
mysql> CREATE TABLE timestamp_val
    -> (
    ->  ts      TIMESTAMP
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>
mysql> INSERT INTO timestamp_val (ts) VALUES('1970-01-01 00:00:00');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO timestamp_val (ts) VALUES('1987-03-05 12:30:15');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO timestamp_val (ts) VALUES('1999-12-31 09:00:00');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO timestamp_val (ts) VALUES('2000-06-04 15:45:30');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> SELECT * FROM timestamp_val;
+---------------------+
| ts                  |
+---------------------+
| 1970-01-01 00:00:00 |
| 1987-03-05 12:30:15 |
| 1999-12-31 09:00:00 |
| 2000-06-04 15:45:30 |
+---------------------+
4 rows in set (0.00 sec)

mysql>
mysql> SELECT ts,
    -> TIME_TO_SEC(ts) AS 'time part in seconds',
    -> SEC_TO_TIME(TIME_TO_SEC(ts)) AS 'time part as TIME'
    -> FROM timestamp_val;
+---------------------+----------------------+-------------------+
| ts                  | time part in seconds | time part as TIME |
+---------------------+----------------------+-------------------+
| 1970-01-01 00:00:00 |                    0 | 00:00:00          |
| 1987-03-05 12:30:15 |                45015 | 12:30:15          |
| 1999-12-31 09:00:00 |                32400 | 09:00:00          |
| 2000-06-04 15:45:30 |                56730 | 15:45:30          |
+---------------------+----------------------+-------------------+
4 rows in set (0.00 sec)

mysql>
mysql>
mysql> drop table timestamp_val;
Query OK, 0 rows affected (0.00 sec)

Related examples in the same category

1.	Breaking Down Time Intervals into Components
2.	TIME_TO_SEC( ) converts a TIME value to the equivalent number of seconds
3.	TIME_TO_SEC(): strips off the date part and returns the time part as the corresponding number of seconds:
4.	To compute the total elapsed time, use TIME_TO_SEC( ) to convert the values to seconds before summing them.
5.	Using TIME_TO_SEC( ) to strip off the date part of the t_create values
6.	Transform the time differences into seconds using TIME_TO_SEC, add them, and then convert them back
7.	To express time values as minutes, hours, or days, perform the appropriate divisions:
8.	Forcing MySQL to Treat Strings as Temporal Values

If you pass TIME_TO_SEC( ) a date-and-time value, it extracts the time part and discards the date. : TIME_TO_SEC « Date Time « SQL / MySQL

Related examples in the same category