If you are already using Perl, modules such as Date::Calc and more in particular Date::Calc::Iterator seems so much more appropriate to solve this problem.

Perhaps because doing it in SQL, you can take advantage of the indexes and groupings the database provides, rather than having to fetch the whole set and then discard data in your script ? For instance, there's 1000 matches for any day within the range, however you want to display them 25 items at a time - do you fetch 1000 items each time, throwing away an unknown amount of records to find the first 25, then do the same on the second page request for the next 25 ? Or would it be more elegant to just ask the database 'records 26-50 matching these criteria, please ?' ?


the hatter

I would say that by using the module Date::Calc::Iterator you are more efficient as you iterate through the set of dates you want and not make a list of all dates and then discard most of them.

Also you don't have to pollute your database with a table of all dates in the range you want.

CountZero

"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law

use strict;
use DateTime::Set;
use DateTime::Format::MySQL;

my ($d1,$d2) = (DateTime->now(),DateTime->now()->add(days=>7));
my $set = DateTime::Set->from_recurrence(
    after => $d1,
    before => $d2,
    recurrence => sub {
        $_[0]->truncate(to=>'day')->add(days=>1)
    },
);

my @dates = map { 
             DateTime::Format::MySQL->format_date($_) 
            } $set->as_list;
# @dates now contains a list of MySQL looking date strings
[download]

# non-production-ready code follows
my ($start_day,$end_day) = $dbh->selectrow_array("select to_days(now()
+), to_days(now() + interval 7 day)");
my @dates = map {
              $dbh->selectrow_array("select from_days($_)")
            } $start_day .. $end_day;
[download]

I am glad you ask the question though, because I am interested in hearing peoples opinions.

Did you already have a look at DateTime::Set?

It can provide you with a set of (recurring) dates extending back from and towards infinity (hey, now all people in the past can start using your module too!)

CountZero

"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law

I agree. To use SQL to select every Wednesday between date X and date Y ought to be trivial. Something like

SELECT * FROM your_table
  WHERE
your_date_column BETWEEN X and Y
  AND
DAYOFWEEK(your_date_column) = 4
[download]

(untested) should do it.

---




($_='kkvvttuu bbooppuuiiffss qqffssmm iibbddllffss')
=~y~b-v~a-z~s; print

Well, that does do it, but you still need a table (your_table) containing a list of dates. What I would like to do is SELECT dates from a table that doesn't really exist. That way I don't have to maintain a table of dates. Is there a way to select dates from a sort of phantom table in MySQL?

Yes, this is a trivial task in mySQL..

And no, you dont need any temporary table...

Here is a simple example (using my own data)

mysql> SELECT send_time, DAYNAME(send_time) AS Day
    -> FROM BillArchive
    -> WHERE send_time BETWEEN '2005-08-02' AND '2005-08-05'
    -> HAVING Day = 'Wednesday'
    -> LIMIT 10;
+---------------------+-----------+
| send_time           | Day       |
+---------------------+-----------+
| 2005-08-03 15:41:40 | Wednesday |
| 2005-08-03 23:08:52 | Wednesday |
| 2005-08-03 16:12:23 | Wednesday |
| 2005-08-03 14:25:40 | Wednesday |
| 2005-08-03 19:50:22 | Wednesday |
| 2005-08-03 20:02:46 | Wednesday |
| 2005-08-03 14:25:40 | Wednesday |
| 2005-08-03 20:02:46 | Wednesday |
| 2005-08-03 22:37:50 | Wednesday |
| 2005-08-03 20:02:46 | Wednesday |
+---------------------+-----------+
10 rows in set (0.09 sec)
[download]

You don't need a temporary table, but you do need a table that actually contains dates to select from. That's easy enough, but what I would really like to do is to select a list of dates from a table that doesn't exist. Similar to how you can SELECT 5+5 and get 10 without selecting from a table. I'd like to be able to say

SELECT date WHERE date BETWEEN start_date AND end_date AND DAY(date)='Wednesday';