Displaying rolls from MySQLi skiping one roll - php

Question

Im looking to display rolls from a MySQLi but I would like to display one yes and one no... example
If I use this code:
$sqldisplay = $mysqli->query("SELECT `id` FROM `albums` ORDER BY `id` DESC LIMIT 5");
while ($rowdisplay = $sqldisplay->fetch_assoc()) {
echo $rowdisplay['id'].'<br>';
}
It will display
10
9
8
7
6
But im looking to display it like this:
10
8
6
4
2
Is it posible? And if so, how can it be done?
Thanks for the help! :D

Answer 1

To display alternating rows, first double your limit.
$sqldisplay = $mysqli->query("SELECT `id` FROM `albums` ORDER BY `id` DESC LIMIT 10");
Then use a boolean switch to determine whether each row will be displayed.
$display = true;
while ($rowdisplay = $sqldisplay->fetch_assoc()) {
if ($display) echo $rowdisplay['id'].'<br>';
$display = !$display; // switch the display on/off
}
This way, you won't have to depend on the value of the ID, something that could produce unexpected results if any IDs are missing due to deleted rows, etc. A numeric ID is a surrogate key which should have no meaning other than uniquely identifying a row.

Answer 2

Using WHERE (id % 2) = 0 would give you only even numbers, and using WHERE (id % 2) > 0 would get you odd numbers.
You can use this along with a subquery that selects MAX(id) and returns either 1 (for odd) or 0 (for even). This will ensure that if the id is even, just even IDs will be returned, and vice-versa, when applied with the logic explained in the paragraph above.
SELECT `id`
FROM `albums`
GROUP BY `id`
HAVING `id` % 2 = (CASE WHEN (SELECT MAX(`id`) FROM `albums`) % 2 = 0 THEN 0 ELSE 1 END)
ORDER BY `id` DESC
LIMIT 5
With Paul's comment below, it's been pointed out that you can clean up the query even more, just doing WHERE id % 2 = (SELECT MAX(id) % 2 FROM albums) instead - this way you shouldn't need any GROUP BY..HAVING.
SELECT `id`
FROM `albums`
WHERE id % 2 = (SELECT MAX(id) % 2 FROM albums)
ORDER BY `id` DESC
LIMIT 5
You can also achieve this in PHP if you wish retrieve both datasets, see Don't Panic's answer for that (although I prefer to do it in MySQL if possible).
MySQL modulus % documentation

Answer 3

when you set id for order by.your result is According to insert each column
you must add column in you table for this .for example you can have column orderBy and you can specify the order of each display column
and then your query same
$sqldisplay = $mysqli->query("SELECT `id` FROM `albums` ORDER BY `orderBy` DESC LIMIT 5");

Answer 4

Simple, just check if the modulo of the ID is 0 (no remainders) to return even numbers.
If you want to return odd numbers, change the modulo to equal 1.
If you want to select odd or even numbers depending on user input, you can easily make an if statement and use Prepared Statements to input the requested number (1 for odd ID rows to be returned, 0 for even rows).
SELECT `id` FROM `albums` WHERE `id` % 2 = 0 ORDER BY `id` DESC LIMIT 5
So your code will be:
$sqldisplay = $mysqli->query("SELECT `id` FROM `albums` WHERE `id` % 2 = 0 ORDER BY `id` DESC LIMIT 5");
while ($rowdisplay = $sqldisplay->fetch_assoc())
{
echo $rowdisplay['id'].'<br>';
}