如何将datetime属性转换为unix timestamp属性？

Question

I want to upgrade my database table by changing the datatype of the column "date_added" from

`date_added` datetime DEFAULT NULL

to

`new_date_added` bigint(20) NOT NULL

date_added has datetime values stored in the format "YYYY-MM-DD HH:MM:SS". This database table has more than 15000 rows. What is the best way to perform this modification?

Note: I have tried executing following MySql query :

ALTER TABLE  `my_table` ADD  `new_date_added` bigint(20) NOT NULL AFTER  `date_added`;
UPDATE `my_table` SET new_date_added = UNIX_TIMESTAMP(  `date_added` );
ALTER TABLE  `my_table` DROP `date_added`;

Above solution doesn't convert datetime value into correct unix_timestamp. If I compare UNIX timestamp created after the modification with its original datetime value, there is a diffrence of 19800 seconds.

Answer 1

19800 seconds = 5:30 hours. You are probably located in India (GMT + 5:30).

UNIX_TIMESTAMP() generates timestamps that are relative to GMT , so it is likely that your values are correct.

To get the right value back, you could eg use PHP's date() and set the correct timezone.

Make sure, however, that you have a really good reason to move away from DATETIME in the first place. It's generally the superior format, allows for all kinds of optimized operations within mySQL, and is free from the year 2038 problem that 32-bit timestamps have.

Answer 2

I found the solution for my problem. Following is the final working code which is giving me correct timestamps :

SET time_zone = "+00:00";
ALTER TABLE  `my_table` ADD  `new_date_added` bigint(20) NOT NULL AFTER  `date_added`;
UPDATE `my_table` SET new_date_added = UNIX_TIMESTAMP(  `date_added` );
ALTER TABLE  `my_table` DROP `date_added`;

@Ela Buwa: I have written the exact same code which is giving me an incorrect timestamp values (due to automatically adjusted/shifted timestamp values)

@Pekka: My question was about mysql's UNIX_TIMESTAMP() giving me unexpected values. Using PHP's date() function will not affect mysql's timezone settings. That is why i used SET time_zone = "+00:00"; to configure mysql's timezone. Thank you for taking a time to answer my question though.

Thank you all for the efforts and sparing your valuable time.

Answer 3

I'd use strtotime. It says the time in the number of seconds passed since 1970-01-01 00:00:00

<?php
echo(strtotime("now") . "<br>");
echo(strtotime("3 October 2005") . "<br>");
echo(strtotime("+5 hours") . "<br>");
echo(strtotime("+1 week") . "<br>");
echo(strtotime("+1 week 3 days 7 hours 5 seconds") . "<br>");
echo(strtotime("next Monday") . "<br>");
echo(strtotime("last Sunday"));
?>

If you want to do it with in mysql, use UPDATE table_name SET timefield=UNIX_TIMESTAMP(timefield); I haven't tested it out though. You might want to check the mysql documents here. http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html