Restrict competition entry to once per day

问题

I'm writing a PHP competition script for a members site that needs to restrict entries to one per day per member. So far I have the following MySQL code:

SELECT ce_id 
  FROM competition_entries 
 WHERE ce_c_id = '$c_id' 
       AND ce_sub_id = '$user_id' 
       AND cte_date >= SYSDATE() - INTERVAL 1 DAY

ce_c_id is the competition ID,
ce_sub_id is the member ID, and
cte_date is a MYSQL datetime stamp for the entry.

It's hard for me to test from where I am now & I need to find a solution, so I'm hoping someone can tell me whether this is restricting to once-per-day or once-per-24hrs - and point me in the right direction if it's the latter.

TIA :)

回答1:

Create a primary key composed of the user_id, competition_id and a date type column.

To check if the user has already placed an entry:

select count(*)
from competition_entries
where ce_c_id = '$c_id' 
    AND ce_sub_id = '$user_id' 
    AND cte_date = current_date()

回答2:

I'm hoping someone can tell me whether this is restricting to once-per-day or once-per-24hrs

Looks like it's 24 hours:

mysql> select sysdate(), sysdate() + interval 1 day;
+---------------------+----------------------------+
| sysdate()           | sysdate() + interval 1 day |
+---------------------+----------------------------+
| 2011-03-21 15:50:56 | 2011-03-22 15:50:56        | 
+---------------------+----------------------------+
1 row in set (0.01 sec)

If you need "tomorrow", as in, tonight at one minute past 23:59, consider chomping down things to plain old DATE's resolution:

mysql> select DATE(sysdate()), DATE(sysdate()) + interval 1 day;
+-----------------+----------------------------------+
| DATE(sysdate()) | DATE(sysdate()) + interval 1 day |
+-----------------+----------------------------------+
| 2011-03-21      | 2011-03-22                       | 
+-----------------+----------------------------------+
1 row in set (0.00 sec)

By just considering dates instead of times, your cutoff will effectively expire at midnight. Watch out, though -- you'll then be at the mercy of the time on your MySQL server, which might differ from the time on your application server if they are on different machines.

回答3:

Can't be sure without testing, but I'd hazard a guess that it's once every 24h.

Try the following instead:

SELECT ce_id FROM competition_entries WHERE ce_c_id = '$c_id' AND ce_sub_id = '$user_id' AND DATE(cte_date) == DATE(SYSDATE())

Here you are clearly comparing two dates, one from your field and the other from the current date for equality.

来源：https://stackoverflow.com/questions/5384649/restrict-competition-entry-to-once-per-day

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