mysql - calculating difference between two times in query

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I know I could use PHP to do this, but wanted to find out if there was a way to calculate the difference between two times using just a query? I tried the query below, but it's returning NULL for the time difference.

The data in my table is stored as:

| created    | changed    |
+------------+------------+
| 1333643004 | 1333643133 |

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I wanted to figure out a way to return:

| 2012-04-05 09:23:24 | 2012-04-05 09:25:33 |     00:02:09 |

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I tried:

SELECT 
    FROM_UNIXTIME(created) AS created, 
    FROM_UNIXTIME(changed) AS changed, 
    TIMEDIFF ( changed, created ) / 60 AS timediff 
FROM content
    WHERE id = 45;

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Which yielded:

| 2012-04-05 09:23:24 | 2012-04-05 09:25:33 | NULL |

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n00b0101Asked:
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Dave BaldwinFixer of ProblemsCommented:
When I tried that, FROM_UNIXTIME is ignored in the TIMEDIFF statement.  TIMEDIFF uses the data from the columns and ignores the 'AS' variables.  Plus I think you had the order wrong in that statement.  And you shouldn't use function names as variable names.

SELECT
    created, changed, (TIMEDIFF ( created, changed ) / 60) AS thediff
FROM content
    WHERE id = 45;
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johanntagleCommented:
timediff requires its inputs to be both datetime or both date datatype.  So it should be:

select timediff(from_unixtime(changed), from_unixtime(created)) from content where id=45;
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johanntagleCommented:
Note also that timediff returns the value in TIME format (hh:mm:ss) so no need to divide by 60.  If you need your result to be something like 1.23 minutes use time_to_sec() (http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_time-to-sec) on the output of timediff then divide by 60.
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