The difference between the creation and modification times

      
mysql>
mysql>
mysql> CREATE TABLE tsdemo2
    -> (
    ->     t_update TIMESTAMP, # record last-modification time
    ->     t_create TIMESTAMP, # record creation time
    ->     val INT
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> INSERT INTO tsdemo2 (t_update,t_create,val) VALUES(NULL,NULL,5);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM tsdemo2;
+---------------------+---------------------+------+
| t_update            | t_create            | val  |
+---------------------+---------------------+------+
| 2011-10-03 13:05:52 | 2011-10-03 13:05:52 |    5 |
+---------------------+---------------------+------+
1 row in set (0.00 sec)

mysql>
mysql> UPDATE tsdemo2 SET val = val + 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT * FROM tsdemo2;
+---------------------+---------------------+------+
| t_update            | t_create            | val  |
+---------------------+---------------------+------+
| 2011-10-03 13:05:52 | 2011-10-03 13:05:52 |    6 |
+---------------------+---------------------+------+
1 row in set (0.00 sec)

mysql>
mysql> SELECT t_create, t_update,
    -> UNIX_TIMESTAMP(t_update) - UNIX_TIMESTAMP(t_create) AS 'seconds',
    -> (UNIX_TIMESTAMP(t_update) - UNIX_TIMESTAMP(t_create))/(60 * 60) AS 'hours'
    -> FROM tsdemo2;
+---------------------+---------------------+---------+--------+
| t_create            | t_update            | seconds | hours  |
+---------------------+---------------------+---------+--------+
| 2011-10-03 13:05:52 | 2011-10-03 13:05:52 |       0 | 0.0000 |
+---------------------+---------------------+---------+--------+
1 row in set (0.00 sec)

mysql>
mysql> drop table tsdemo2;
Query OK, 0 rows affected (0.00 sec)

mysql>

Related examples in the same category

1.	TIMESTAMP as column type
2.	timestamp type column default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP
3.	Table definition includes a YEAR column and a TIMESTAMP
4.	Order by timestamp value
5.	dates and times in SQL commands must be given as character strings,
6.	Recording a Row's Last Modification Time
7.	Recording a Row's Creation Time
8.	Performing Calculations with TIMESTAMP Values
9.	Updates to tsdemo2 records that don't actually modify a column cause no change to TIMESTAMP values
10.	Create a table in which timestamps can be stored.
11.	Issuing an UPDATE statement that doesn't actually change the values in the val column doesn't update the TIMES
12.	microseconds component is removed.

The difference between the creation and modification times : TimeStamp « Data Type « SQL / MySQL

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