Should I use the datetime or timestamp data type in MySQL?

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Top 5 Answer for Should I use the datetime or timestamp data type in MySQL?

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99

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.

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82

In MySQL 5 and above, TIMESTAMP values are converted from the current time zone to UTC for storage, and converted back from UTC to the current time zone for retrieval. (This occurs only for the TIMESTAMP data type, and not for other types such as DATETIME.)

By default, the current time zone for each connection is the server's time. The time zone can be set on a per-connection basis, as described in MySQL Server Time Zone Support.

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76

I always use DATETIME fields for anything other than row metadata (date created or modified).

As mentioned in the MySQL documentation:

The DATETIME type is used when you need values that contain both date and time information. MySQL retrieves and displays DATETIME values in 'YYYY-MM-DD HH:MM:SS' format. The supported range is '1000-01-01 00:00:00' to '9999-12-31 23:59:59'.

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The TIMESTAMP data type has a range of '1970-01-01 00:00:01' UTC to '2038-01-09 03:14:07' UTC. It has varying properties, depending on the MySQL version and the SQL mode the server is running in.

You're quite likely to hit the lower limit on TIMESTAMPs in general use -- e.g. storing birthdate.

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62

The below examples show how the TIMESTAMP date type changed the values after changing the time-zone to 'america/new_york' where DATETIMEis unchanged.

mysql> show variables like '%time_zone%'; +------------------+---------------------+ | Variable_name    | Value               | +------------------+---------------------+ | system_time_zone | India Standard Time | | time_zone        | Asia/Calcutta       | +------------------+---------------------+  mysql> create table datedemo(     -> mydatetime datetime,     -> mytimestamp timestamp     -> );  mysql> insert into datedemo values ((now()),(now()));  mysql> select * from datedemo; +---------------------+---------------------+ | mydatetime          | mytimestamp         | +---------------------+---------------------+ | 2011-08-21 14:11:09 | 2011-08-21 14:11:09 | +---------------------+---------------------+  mysql> set time_zone="america/new_york";  mysql> select * from datedemo; +---------------------+---------------------+ | mydatetime          | mytimestamp         | +---------------------+---------------------+ | 2011-08-21 14:11:09 | 2011-08-21 04:41:09 | +---------------------+---------------------+ 

I've converted my answer into article so more people can find this useful, MySQL: Datetime Versus Timestamp Data Types.

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52

The main difference is that DATETIME is constant while TIMESTAMP is affected by the time_zone setting.

So it only matters when you have — or may in the future have — synchronized clusters across time zones.

In simpler words: If I have a database in Australia, and take a dump of that database to synchronize/populate a database in America, then the TIMESTAMP would update to reflect the real time of the event in the new time zone, while DATETIME would still reflect the time of the event in the au time zone.

A great example of DATETIME being used where TIMESTAMP should have been used is in Facebook, where their servers are never quite sure what time stuff happened across time zones. Once I was having a conversation in which the time said I was replying to messages before the message was actually sent. (This, of course, could also have been caused by bad time zone translation in the messaging software if the times were being posted rather than synchronized.)

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