Inserting new entry and updating a whole column at the same time - php

Question

I have a somewhat complex problem that needs fixing, for now I have the following table structure (task_schedule):
id taskid productid product_position
1 1 1 1
2 2 1 2
3 3 2 1
4 4 1 3
5 5 2 2
6 6 3 1
product_position works the following way: it should look at the productid and increment from the previous max value entry.
I accomplish this with the following query (probably easier to understand too):
INSERT into task_schedule (taskid, productid, product_position)
SELECT 1,1, max(product_position) + 1
FROM task_schedule
WHERE productid=1
(the values are of course attributed in the php backend)
I need a new column now though. Lets call it user_position, I'm going to recreate my table with an example:
id taskid productid product_position user_position
1 1 1 1 1
2 2 1 2 4
3 3 2 1 2
4 4 1 3 6
5 5 2 2 5
6 6 3 1 3
OK, so how this should work is: user_position should individually run through each entry and look at the productid, it should build a position list based on an even order of priority.
So if I ordered this by user_position I would get the following entry id list: 1 3 6 2 5 4
An example of what I need done in php:
Imagine the following list: red red red green green green green blue blue yellow
$array1 = array(array("red"), array("red"), array("red"));
$array2 = array(array("green"), array("green"), array("green"), array("green"));
$array3 = array(array("blue"), array("blue"));
$array4 = array(array("yellow"));
$Arrays= array ($array1, $array2, $array3, $array4);
foreach ($Arrays as $type => $list) {
$ArrayLength[]=count($list);
}
$MergeArray=array();
$flag=true;
for($i=0;$flag==true;$i++)
{
$flag=false;
for($j=0;$j < count($ArrayLength);$j++)
{
if( $i < $ArrayLength[$j] )
{
array_push( $MergeArray , $Arrays[$j][$i] );
$flag=true;
}
}
}
echo "<pre>".Print_r(json_encode($MergeArray), true)."</pre>";
This returns me a consistent list with the pattern I desire:
[["red"],["green"],["blue"],["yellow"],["red"],["green"],["blue"],["red"],["green"],["green"]]
All of the above is just an example of what I need, but implemented via MySQL.
I don't even know how to approach this issue now though, I need a way to insert new entries AND update the user_position column accordingly.
If I was to add a new entry into my table, with a new peoduct_id, this should be the end result:
id taskid productid product_position user_position
1 1 1 1 1
2 2 1 2 5
3 3 2 1 2
4 4 1 3 7
5 5 2 2 6
6 6 3 1 3
7 7 4 1 4
Notice how the user_position shifted to accommodate the new row.
I think this is a fairly complex problem to solve (or maybe my mysql is just THAT weak), I don't think there is a easy solution for this one, so any input you might have on how to approach this via mysql (mysql doing the heavy lifting would be fantastic), but I welcome a PHP solution as well with multiple queries and whatnot. Unfortunately I can't drop this column, it's easy to grab entries and let PHP sort my information, but I really need this implemented in the database.
Any input from the community would be great really.

Answer 1

Insert using the normal insert query which you are using
INSERT into task_schedule (taskid, productid, product_position, user_position)
SELECT 1,1, max(product_position) + 1, 0 FROM task_schedule WHERE productid=1;
And then update all the entries based on product_position using the below
SET #counter = 0;
UPDATE task_schedule SET user_position = #counter := #counter + 1 ORDER BY product_position asc, productid asc;
Here is the SQL fiddle link