Implode ids within a while loop and add commas between - php

Question

I'm trying to display some sub-content so I need to get the child id's of their parent.
This is how I wanted to do it:
$ids = "SELECT * FROM `web_categories` WHERE parent_id = 14 AND published = 1";
$idscon = $conn->query($ids);
while ($ids = $idscon->fetch_array()){
$idss .= $ids['id'];
}
$project1 = "SELECT * FROM `web_content` WHERE catid in ('$idss') AND state = 1";
$projectcon1 = $conn->query($project1);
$projectcr1 = array();
while ($projectcr1[] = $projectcon1->fetch_array());
I tried imploding $idss like this:
$implode = implode(',', $idss);
But this gives me Invalid arguments passed. What am I doing wrong?

Answer 1

You are doing wrong in the first while loop.
Here it is, $idss .= $ids['id'];, You are doing wrong this. You are storing value in a variable as string, but when you try to implode this... It throws an error!!! Cause implode() use to make array into string. So follow the below steps.
Change $idss .= $ids['id']; to $idss[] = $ids['id']; and instead of implode() use the join().
Create an array names $idss, and push or insert the ids into that array. Then implode/join that IDs.
$idss = array();
while ($ids = $idscon->fetch_array()){
$idss[] = $ids['id'];
}
$implode = implode(',', $idss);
Now you can use this $implode variable in the next query.

Answer 2

You just need to store all IDs in an array, something like $yourIDs[] = $ids['id']; inside your first while loop.
With $idss .= $ids['id']; you can't use implode() because result of this action should be something like "1234" without any single comma.
You just need to use like that:
<?php
$yourIDs = array();
while ($ids = $idscon->fetch_array()){
$yourIDs[] = $ids['id']; // this will save all IDs into $yourIDs array.
}
$idss = implode(',',$yourIDs); // result of this should be 1,2,3,4 etc.
?>

Answer 3

I think you could most likely do that in one query
SELECT * FROM `web_content` WHERE `catid` in (
SELECT `id` FROM `web_categories` WHERE `parent_id` = 14 AND `published` = 1
) AND `state` = 1
The original code was, in effect, doing exactly this but in two stages - sub-queries can be slow sometimes but it does depend on the size of the db and the number of expected results. It is true that joins can be and generally are more efficient than dependant subqueries so perhaps that is another option to explore. As mysql executes the query plan from the outside to the inside rather than the intuitive inside to outside subqueries can cause the server to crawl - it really depends on the complexity of the subquery and the amount of data that has to be processed.