Brian,

It depends on how you determine submission date. If you take it from the header in the email client which receives the entry, it depends on how your email client determines the date. You could bypass all this variability by always inserting entries in the order in which they arrive. But that's lossy  To preserve the email handler's version of the time, but still avoid the sort of date arithmetic complications you originally asked about, translate entry email-receive time into UTC time, which as you see is simple arithmetic, and do your serverside date arithmetic in UTC time.

PB

-----

Thanks Sheeri, but now I'm a bit more confused. Does that mean that the
scenario that I listed below does not work even if I use UTC_TIMESAMP?
That's what I still don't get, if someone on the east coast submits their
test, and the web code on my server (which is on the west coast) is what
actually performs the INSERT using UTC_TIMESTAMP, then it seems like this
still doesn't work. This is driving me crazy :-) Any ideas? Is the bottom
line that I have to have a specific time zone for each student in my
database so I can do comparisons that way? 

I'm thinking about webex and how they send emails that automatically adjusts
for time zones. I think at some point, I had to tell them what time zone I
was in. I see that a lot on the web. Seems like a pain, but I don't see any
way around it.

-Brian

-----Original Message-----
From: sheeri kritzer [mailto:awfief@gmail.com] 
Sent: Thursday, May 25, 2006 9:13 AM
To: Brian Menke
Cc: peter.brawley@earthlink.net; mysql@lists.mysql.com
Subject: Re: Fun with Dates and Incentives.

Brian,

MySQL's timestamp function is based on the *server*'s timestamp, not
the client's.

-Sheeri

On 5/24/06, Brian Menke <brian@innovtech.com> wrote:
  
Wow, if I read that right, it means someone on the East coast submits
answers to a test, it's somehow adjusted to be the same as someone who
submits answers to a test from the west coast 3 hours later (time zone
wise)? I can't possibly imagine how that works, but if it does that solves
huge problems for me and I seriously owe you! I'm gonna do some more
research so I understand how this works.



THANKS!



-Brian



  _____

From: Peter Brawley [mailto:peter.brawley@earthlink.net]
Sent: Wednesday, May 24, 2006 3:56 PM
To: Brian Menke
Cc: mysql@lists.mysql.com
Subject: Re: Fun with Dates and Incentives.



Brian,

CURRENT_TIMESTAMP gives you time in your server's timezone. UTC_TIMESTAMP
gives GM (universal) time, so dispenses with all timezone adjustments.
Trouble is, you cannot use it as a defalt. You have to pass it as an
    
INSERT
  
value.

PB

-----

Brian Menke wrote:

Peter, thanks for the detailed info. I will figure out how to get rid of
    
the
  
UNIQUE key. Somehow that got added. Thanks for the catch. As far as INT
    
for
  
student id goes, I'm using email because it will be unique, and offers an
easy way to track a user through the app I'm building (user name,
    
password,
  
session id's etc.) but I do get what you are saying. Thanks for the
UTC_TIMESTAMP suggestion. Although, since I haven't had a lot of
    
experience,
  
I don't really understand why it is better than CURRENT_TIMESTAMP. But.
that's why I asked for advice :-)



-Brian



  _____

From: Peter Brawley [mailto:peter.brawley@earthlink.net]
Sent: Wednesday, May 24, 2006 1:31 PM
To: Brian Menke
Cc: mysql@lists.mysql.com
Subject: Re: Fun with Dates and Incentives.



Brian

Re your schema,
  --it's redundant to define PRIMARY and UNIQUE keys on the same column,
  --why not an INT student id?
  --what if two (eg married) students share an email account?
  --comparing datetimes across multiple time zones will be simpler if you
    set completed_modules.time=UTC_TIMESTAMP in each new row of that
    
table.
  
That would give ...

CREATE TABLE students (
  id INT NOT NULL,        -- auto_increment [simplest] or assigned by
school?
  email varchar(64) NOT NULL,
  fname varchar(32) NOT NULL,
  lname varchar(32) NOT NULL,
  role char(2) NOT NULL default '5',
  password varchar(8) NOT NULL,
  phone varchar(24) default NULL,
  reg_date date default NULL,
  PRIMARY KEY (id),
  KEY email (email)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

CREATE TABLE completed_modules (
  id INT NOT NULL,
  module_id char(2) NOT NULL default '',
  score INT NOT NULL default 0,
  time timestamp NOT NULL default CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

To find the first 10 scores of 100 on a particular module, just ...

SELECT
  CONCAT(s.lname,', ',s.fname) AS Name,
  c.time,
  c.score
FROM students s
INNER JOIN completed_modules c USING (id)
WHERE c.module_id = 1 AND c.score = 100
ORDER BY c.time ASC
LIMIT 10;

PB





I'm hoping for some general advice on an approach for the following
scenario:



I have a customer who wants to put an incentive program in place for
students taking learning modules and then completing tests. The concept is
simple. Award the first 10 people who complete a test with a score of
100%... that type of thing. Students are allowed to take test more than
once. Track each time the student takes the test and show the latest score
ect. You get the idea. I have the database tables and relationships
    
already
  
all set up for the tests, but it's the tracking of the dates and times
    
that
  
I don't have and it got me thinking.



I need to track down to the day/hour/minute level. Okay, that should be
    
easy
  
(I think). I'm going to need to do a lot of date/time calculations. Would
    
it
  
be best just to have a default of CURRENT_TIMESTAMP set for a TIMESTAMP
field? Or, is their something else I should be using? I have limited
experience having to munge and crunch date/time info and I want to make
    
sure
  
I have the flexibility to do what I need in the future.



The next gotcha I thought up is what about different time zones. Obviously
without this consideration, people on the East coast would have an unfair
    
3
  
hour advantage over people on the west coast. I guess I can have a time
    
zone
  
field in my student table so I could derive the time difference. Any
suggestions on a good time zone approach?



Here are my two tables as they stand now. I'm wondering if these are set
    
up
  
in a way to allow me to do all this date time crunching I'm going to need
    
to
  
do in the future? Any suggestions are greatly appreciated :-)





CREATE TABLE `students` (

  `store_id` varchar(6) NOT NULL,

  `email` varchar(64) NOT NULL,

  `fname` varchar(32) NOT NULL,

  `lname` varchar(32) NOT NULL,

  `role` char(2) NOT NULL default '5',

  `password` varchar(8) NOT NULL,

  `phone` varchar(24) default NULL,

  `reg_date` date default NULL,

  PRIMARY KEY  (`email`),

  UNIQUE KEY `email` (`email`)

) ENGINE=InnoDB DEFAULT CHARSET=latin1;



CREATE TABLE `completed_modules` (

  `module_id` char(2) NOT NULL default '',

  `email` varchar(64) NOT NULL,

  `score` int(2) NOT NULL default '0',

  `time` timestamp NOT NULL default CURRENT_TIMESTAMP

) ENGINE=InnoDB DEFAULT CHARSET=latin1;



Brian Menke

Visual Matter, Inc

1445 Foxworthy Ave., Suite 50-215

San Jose, CA 95118

408 375 9969



San Jose ~ Los Angeles
www.visualmatter.com













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