Shantanu's Blog

Corporate Consultant

August 21, 2010

 

3 reasons to avoid timestamp

Here are 3 reasons why you should avoid "timestamp" column type.

1) Range: It can store values only from 1st Jan 1970 to 31 Dec 2037. This range is not enough for most applications.

2) On update clause:
As you can see from the following screen, I specified only a "timestamp" column type in the create table statement. MySQL silently added the "on update CURRENT_TIMESTAMP". When I tried to update a column, the value of "mytime" column was changed as well from 02 to 33 (seconds). This is unexpected behavior for a novice coder.

mysql>use test;
mysql>create table stamptest(id int, name varchar(100), mytime timestamp);
Query OK, 0 rows affected (0.03 sec)

mysql>show create table stamptest\G
*************************** 1. row ***************************
Table: stamptest
Create Table: CREATE TABLE `stamptest` (
`id` int(11) default NULL,
`name` varchar(100) default NULL,
`mytime` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP
) ENGINE=MyISAM DEFAULT CHARSET=latin1
1 row in set (0.01 sec)

mysql>insert into stamptest values (1, 'john', NULL);
Query OK, 1 row affected (0.01 sec)

mysql>select * from stamptest;
+------+------+---------------------+
| id | name | mytime |
+------+------+---------------------+
| 1 | john | 2010-08-21 06:21:02 |
+------+------+---------------------+
1 row in set (0.00 sec)

mysql>update stamptest set name = 'abcd' where id = 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0

(06:21) mysql>select * from stamptest;
+------+------+---------------------+
| id | name | mytime |
+------+------+---------------------+
| 1 | abcd | 2010-08-21 06:21:33 |
+------+------+---------------------+
1 row in set (0.00 sec)


3) Back-up using dump
The time saved in the timestamp column will get adjusted to the timezone of the server from where you are trying to run the mysqldump command.
The --skip-tz-utc switch needs to be added to the dump command and most people are unaware of this.

http://dev.mysql.com/doc/refman/5.1/en/mysqldump.html#option_mysqldump_tz-utc

The only advantage that I can see is that it consumes 4 bytes compared to datetime's 8 bytes. This does not make much difference to most general purpose applications.

The poor PHP programmers have their own deadlines and are less interested in learning these things. Do not use "timestamp" column type and avoid using from_unixtime() and unix_timestamp() functions to save datetime at any cost. The only option left to save the date+time is... what else? "datetime"!!

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Comments:
I prefer to use TimeStamp column to set/get default current timestamp for the record if there is any insert or update. I believe that's the best use of TimeStamp column and I think TimeStamp is the only option to set the default timestamp in MySQL, I am not sure if there is any other alternative.

for all other datetime related columns I use DateTime datatype which I am updating through code etc.
 
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