Posted by Oli Filth on 07/07/38 11:28

meltedown said the following on 04/10/2005 22:50:
> Oli Filth wrote:
>
>> meltedown said the following on 04/10/2005 18:40:
>>
>>>>> Why doesn't this return anything ?
>>>>>
>>>>> SELECT DATE_SUB('FROM_DAYS(TO_DAYS(2005-09-28 18:04:19))', INTERVAL
>>>>> 6 DAY)
>>>>
>>>
>>> I'm trying to get the date that's a week before the date in the query.
>>
>>
>> If you had bothered to RTFM, you would've found that you can put the
>> date straight into DATE_SUB (seeing as FROM_DAYS(TO_DAYS()) gets you
>> back where you started, assuming you had the syntax correct).
>
>
> I've tried to read the date functions section but it is written in
> neo-colonial greek. That's early greek, before Athens was even a city.
> I've got all the best books, and they aren't much better.

I agree, the manual is somewhat dense and cryptic, but there are *lots*
of examples, including one as follows:

SELECT DATE_SUB('1998-01-02', INTERVAL 31 DAY)
>
>>
>> Note also that a week is 7 days long!
>>
>> SELECT DATE_SUB('2005-09-28 18:04:19', INTERVAL 7 DAY)
>>
>> If you don't want the time in the result, then cast it to a DATE, i.e.:
>>
>> SELECT DATE(DATE_SUB('2005-09-28 18:04:19', INTERVAL 7 DAY))
>>
>>
> Thanks, that seems to work. The other worked for a long time, I don't
> know why it would work and then not work. The only thing different was
> the date.

Your original query (with the quotes where they were) could never have
worked, as 'FROM_DAYS(TO_DAYS(2005-09-28 18:04:19))' is not a valid date
string. ;)

All it does is truncate the invalid date string to nothing, and hence
you will get a NULL return value.


--
Oli

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