There is a manual page on Time and Date functions.
The best way to compare date and time and get minutes back is probably to use one of the following:
SELECT TIME_TO_SEC(TIMEDIFF(timea,timeb)+0)/60
SELECT TIMESTAMPDIFF(MINUTE,timeb,timea)
Note that while TIMEDIFF
works with times, TIMESTAMPDIFF
requires a date component - and the values are switched around for TIMESTAMPDIFF
.
You can return hours with either of these:
SELECT TIME_TO_SEC(TIMEDIFF(timea,timeb)+0)/60/60
SELECT TIMESTAMPDIFF(HOUR,timeb,timea)
Note that when using DATEDIFF
, the value returned is a difference between the date components of the given time - thus, a value of 23:59 on one day compared to a value of 0:01 on the next (a 2 minute difference) results in a date difference of 1 (a full day).
To get a difference between two times in 24-hour periods (length of a day) first calculate the difference in minutes then divide by the proper values to find the number of 24-hour periods. Try this:
SELECT TRUNCATE(TIMESTAMPDIFF(MINUTE,timeb,timea)/60.0/24.0,0)
This truncates the decimal portion, returning only the number of complete 24-hour periods in the specified timespan.
To go along with @ypercube's comment that CURRENT_TIMESTAMP
is stored as UTC but retrieved as the current timezone, you can affect your server's timezone setting with the --default_time_zone option for retrieval. This allows your retrieval to always be in UTC.
By default, the option is 'SYSTEM' which is how your system time zone is set (which may or may not be UTC!):
mysql> SELECT @@global.time_zone, @@session.time_zone;
+--------------------+---------------------+
| @@global.time_zone | @@session.time_zone |
+--------------------+---------------------+
| SYSTEM | SYSTEM |
+--------------------+---------------------+
1 row in set (0.00 sec)
mysql> SELECT CURRENT_TIMESTAMP();
+---------------------+
| CURRENT_TIMESTAMP() |
+---------------------+
| 2012-09-25 16:28:45 |
+---------------------+
1 row in set (0.00 sec)
You can set this dynamically:
mysql> SET @@session.time_zone='+00:00';
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT @@global.time_zone, @@session.time_zone;
+--------------------+---------------------+
| @@global.time_zone | @@session.time_zone |
+--------------------+---------------------+
| SYSTEM | +00:00 |
+--------------------+---------------------+
1 row in set (0.00 sec)
Or permanently in your my.cnf:
[mysqld]
**other variables**
default_time_zone='+00:00'
Restart your server, and you will see the change:
mysql> SELECT @@global.time_zone, @@session.time_zone;
+--------------------+---------------------+
| @@global.time_zone | @@session.time_zone |
+--------------------+---------------------+
| +00:00 | +00:00 |
+--------------------+---------------------+
1 row in set (0.00 sec)
mysql> SELECT CURRENT_TIMESTAMP();
+---------------------+
| CURRENT_TIMESTAMP() |
+---------------------+
| 2012-09-25 20:27:50 |
+---------------------+
1 row in set (0.01 sec)
Best Answer
Alright... after a change in my approach, I decided to try to "extract" data instead of convert. Turned out there's the oh-so convenient function
extract
in Postgres, which does exactly what I want.extract(EPOCH from my_date_column) as date_timestamp
Here is a more detailed explanation.