MySQL Server – Set max_allowed_packet value permanently

IMPORTANT EDIT: It is now possible to achieve this with DATETIME fields since MySQL 5.6.5, take a look at the other post below...

Previous versions can't do that with DATETIME...

But you can do it with TIMESTAMP:

mysql> create table test (str varchar(32), ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP);
Query OK, 0 rows affected (0.00 sec)

mysql> desc test;
+-------+-------------+------+-----+-------------------+-------+
| Field | Type        | Null | Key | Default           | Extra |
+-------+-------------+------+-----+-------------------+-------+
| str   | varchar(32) | YES  |     | NULL              |       | 
| ts    | timestamp   | NO   |     | CURRENT_TIMESTAMP |       | 
+-------+-------------+------+-----+-------------------+-------+
2 rows in set (0.00 sec)

mysql> insert into test (str) values ("demo");
Query OK, 1 row affected (0.00 sec)

mysql> select * from test;
+------+---------------------+
| str  | ts                  |
+------+---------------------+
| demo | 2008-10-03 22:59:52 | 
+------+---------------------+
1 row in set (0.00 sec)

mysql>

CAVEAT: IF you define a column with CURRENT_TIMESTAMP ON as default, you will need to ALWAYS specify a value for this column or the value will automatically reset itself to "now()" on update. This means that if you do not want the value to change, your UPDATE statement must contain "[your column name] = [your column name]" (or some other value) or the value will become "now()". Weird, but true. I am using 5.5.56-MariaDB

Timestamps in MySQL are generally used to track changes to records, and are often updated every time the record is changed. If you want to store a specific value you should use a datetime field.

If you meant that you want to decide between using a UNIX timestamp or a native MySQL datetime field, go with the native format. You can do calculations within MySQL that way ("SELECT DATE_ADD(my_datetime, INTERVAL 1 DAY)") and it is simple to change the format of the value to a UNIX timestamp ("SELECT UNIX_TIMESTAMP(my_datetime)") when you query the record if you want to operate on it with PHP.