If a row is not unique - ignore it - php - php

Question

I'm working on the following code:
function form_Subcat_Picker() {
$mysqli = new mysqli(DB_SERVER, DB_USER, DB_PASSWORD, DB_NAME);
if (!$mysqli) {
die('There was a problem connecting to the database.');
}
$catPicker = "SELECT Subcatid, Subcatname, Parentid
FROM ProductSubCats
ORDER BY Subcatid";
if ($Result = $mysqli->query($catPicker)){
if (!$Result) {
echo 'Could not run query: ' . mysql_error();
exit;
}
while ($row = $Result->fetch_assoc()) {
echo '<div class="parentid'.$row['Parentid'].'">';
echo '<select name="Subcatid">';
echo '<option value="'.$row["Subcatid"].'">'.$row["Subcatname"]."</option>";
echo '</select>';
echo '</div>';
}
}
$mysqli->close();
}
What I want to do, is in the line:
while ($row = $Result->fetch_assoc()) {
echo '<div class="parentid'.$row['Parentid'].'">';
If the $row['Parentid'] part is the same as the previous iteration, I want to ignore that particular line (adding the div class)
So that if for example in the first run $row['Parentid'] is 1, and in the next loop it is 1 again, I want to not create a new div, just echo everything else and thus keep it in the same div.
Is this possible? Alternatively, how could I make multiple sub category id's and names appear in the one div, if they share a common parentid (there are multiple parent ids)
For the line:
echo '<option value="'.$row["Subcatid"].'">'.$row["Subcatname"]."</option>";

Answer 1

Maybe this would work:
$last_id = 0;
while ($row = $Result->fetch_assoc()) {
if ($last_id != $row['Parentid']) {
echo '<div class="parentid'.$row['Parentid'].'">';
echo '<select name="Subcatid">';
echo '<option value="'.$row["Subcatid"].'">'.$row["Subcatname"]."</option>";
echo '</select>';
echo '</div>';
$last_id = $row['Parentid'];
}
}
However, I think the best solution is to filter them out in the SQL statement, maybe the GROUP BY clause, but I'm not 100% sure how to do it :).
Regards,

Answer 2

That is just something basic for looping. Let's see your current loop:
while ($row = $Result->fetch_assoc()) {
...
}
As you want to skip with a specific condition, let's just introduce this skipping (not taking much care about the condition first):
while ($row = $Result->fetch_assoc()) {
if ($condition) continue;
...
}
Now let's formulate the condition. As we want to look into the last $row we need to keep a copy:
$last = null;
while ($row = $Result->fetch_assoc()) {
if ($condition) continue;
...
$last = $row;
}
Now we've got the data we need to have to create the condition, $last can contain the last row (if there was one) and therefore the comparison can be done:
$last = null;
while ($row = $Result->fetch_assoc()) {
$condition = $last && $row['Parentid'] === $last['Parentid'];
if ($condition) continue;
...
$last = $row;
}
And that is it basically. Depending on the logic, you might want to switch to a for loop:
for ($last = null; $row = $Result->fetch_assoc(); $last = $row) {
$condition = $last && $row['Parentid'] === $last['Parentid'];
if ($condition) continue;
...
}
This for example does ensure that for each iteration (even the skipped ones), the $last is set to the $row at the end of the loop.
Instead of continue you can naturally do different things, like not outputting the <div> or similar.
Hope this helps.

Answer 3

This is the way I'd write it.
// add a variable to hold the previous value
$previous_parent_id = "";
while ($row = $Result->fetch_assoc()) {
// then add an if statement to see if it's the previous statement
if ($row['parent_id'] != $previous_parent_id){
echo '<div class="parent_id'.$row['parent_id'].'">';
$previous_parent_id = $row['parent_id'];
}
}
So going in a loop on these records
ID ParentID
1 0
2 0
3 1
4 1
4 2
4 2
the output would be:
<div class="parent_id0">
<div class="parent_id1">
<div class="parent_id2">