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I want to add x days to a datetime


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#1 shaggycap

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Posted 10 February 2006 - 03:51 PM

I have a field in my DB called 'trial_start' which is a datetime with a default value of now().

There is another field in the DB called 'days' which is the no of days that the trial will run for.

I want another field, called 'trial_end' which is, you've guessed it, the 'trial_start' plus the number of days.

I am struggling as to what syntax to use, to calculate the 'trial_end' value. I assume I need to turn the days into seconds and add them onto the timestamp of the trial_start.

Can anyone help please as I'm struggling. Thanks

#2 fenway

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Posted 10 February 2006 - 07:50 PM

My first question is why store all three? You only need two of them, and the 3rd can always be calculated. Second, how much sense does it make to add a fixed number of days to a DATETIME column -- doesn't that mean the time of the trial_end value is meaningless?

Anyway, regardless, you can always use INTERVAL to set it (UNTESTED):

UPDATE yourTable SET trial_end = trial_start + INTERVAL days DAY WHERE....

Hope that helps.
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#3 obsidian

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Posted 10 February 2006 - 07:58 PM

... or, just do them all at once:

[!--sql--][div class=\'sqltop\']SQL[/div][div class=\'sqlmain\'][!--sql1--][span style=\'color:blue;font-weight:bold\']UPDATE[/span] tableName SET trial_end = DATE_ADD(trial_start, INTERVAL days DAY);
[!--sql2--][/div][!--sql3--]
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