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trying to understand INTERVAL

Thread began 2/20/2015 1:29 am by Jamie | Last modified 2/20/2015 11:11 am by Jason Byrnes | 597 views | 3 replies |


trying to understand INTERVAL

Hey Jason

Am trying to understand a MYSQL statement

"SELECT *, member_info.* FROM presentations INNER JOIN member_info ON MemberNameID = MemberID WHERE Live = 1 AND DATE_FORMAT(PresentationDate, '%Y-%m-%d') >= (CURDATE() + INTERVAL 0 HOUR) ORDER BY PresentationDate ASC"

The bit I am trying to understand is


- basically I am trying to undestand what changing the 0 HOUR to 1 HOUR is actually doing as at the moment set to 0 content using, for example todays date, shows the content for todays date but if I change it to 1 HOUR the content for todays date is no longer visible.

Is this a binary 1 or 0 (ie off / on) or is it a number and could be anything from 0 to 24?



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Jason ByrnesWebAssist

honestly the expression does not make any sense as it is used in this query.

CURDATE() returns the date in yyyy-mm-dd format:

(CURDATE() + INTERVAL 0 HOUR) returs the current date, but adds the time as well in the format yyyy-mm-dd hh:ii:ss
2015-02-20 00:00:00

setting the interval to 1 hour adds an hour to the time:
2015-02-20 01:00:00

So, why do i say it doesn't make any sense to add the interval you ask. . .

well because the value you are comparing to does not contain the time any way:

DATE_FORMAT(PresentationDate, '%Y-%m-%d')

this value is formatted as yyyy-dd-mm already

so, if that value returns todays date the where clause:
DATE_FORMAT(PresentationDate, '%Y-%m-%d') >= (CURDATE() + INTERVAL 0 HOUR)

would mean:
2015-02-20 >= 2015-02-20 00:00:00

which evaluates to true, but really the time portion is not needed. you could just as easily do:
DATE_FORMAT(PresentationDate, '%Y-%m-%d') >= CURDATE()

which would mean:
2015-02-20 >= 2015-02-20

Now if you add 1 hour:
DATE_FORMAT(PresentationDate, '%Y-%m-%d') >= (CURDATE() + INTERVAL 1 HOUR)

now the comparison becomes:
2015-02-20 >= 2015-02-20 01:00:00

which is false

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thanks so much Jason, that really helps me understand if!

have a great weekwnd


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Jason ByrnesWebAssist

you're welcome

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