php / mysql, need advice on method to store this data - php

Question

Basically on my website there are checkboxes for each day of the week. If a user checks them, those are the days to be saved (in a field) in their user account.
How would I go about saving these dates? For example, if someone checks Saturday and Wednesday, another saves Monday and Tuesday, what's a good pattern to keep this info?
Someone suggested saving it as a bit string like 0001001 the 1's representing the days of the week check marked, out of the 7 bits representing each day. Any ideas?
The table would look like this:
user_id | days
10 | 0010010 (Wednesday and Saturday, week starts on Monday)
The only issue with is how would I output this info from php?
(I'm trying to do this in the most optimal way both on the mysql and php side)

Answer 1

The suggestion to use a bit field type in MySQL with a length of seven sounds fair to keep storage requirements low (BIT(7)).
The only issue with is how would I output this info from php?
The first step would be to define a mapping of each bit to a weekday-name:
$days = array(
'Monday',
'Tuesday',
...
'Sunday'
);
Then you first need to select the binary value from the database, e.g. as a decimal (integer) value:
SELECT days+0 FROM table;
In PHP you can convert this to a fixed-width binary number string using decbin and substr:
$binary = substr('000000'.decbin($integer), -7);
or probably more convenient sprintf:
$binary = sprintf('%07b', $integer);
As each of those characters is either 0 or 1 you can iterate over them and create an array for all set days:
$array = array();
foreach (range(0, 7) as $day)
{
if (! $set = (int) $binary[$day])
continue;
$array[] = $days[$day];
}
The resulting $array contains now all weekday names that the user checked. You can then output them:
$output = '(none)';
if (1 === $count = count($array)
{
$output = $array[0]; # one day
}
elseif ($count)
{
$last = array_pop($array); # last day
$output = implode(', ', $array) . ' and ' . $last;
}
That was the output of the database value. Hope this is helpful.

Answer 2

You can store the days in a serialized array, and that way, get it back easily when you want it.
$days = array('wednesday','saturday');
$store = serialize($days);
and then store $store for that user_id

Answer 3

I think it would be easier to store like this:
user_id | sun | mon | tues | wed |...
01 | 1 | 0 | 0 | 1 |
And leave the day columns as tinyint(1)'s. That way, in PHP, you could just go like this:
if($row['sun'] == 1)
Do sunday stuff

Answer 4

I would suggest a table like this:
id user_id day
1 1 1
2 1 4
3 2 1
4 3 7