Create SQL query that orders results by which condition they meet

Question

This is for MySQL and PHP

I have a table that contains the following columns:

navigation_id (unsigned int primary key)
navigation_category (unsigned int)
navigation_path (varchar (256))
navigation_is_active (bool)
navigation_store_id (unsigned int index)

Data will be filled like:

1, 32, "4/32/", 1, 32
2, 33, "4/32/33/", 1, 32
3, 34, "4/32/33/34/", 1, 32
4, 35, "4/32/33/35/", 1, 32
5, 36, "4/32/33/36/", 1, 32
6, 37, "4/37/", 1, 32
... another group that is under the "4/37" node
... and so on

So this will represent a tree like structure. My goal is to write a SQL query that, given the store ID of 32 and category ID of 33, will return

First, a group of elements that are the parents of the category 33 (in this case 4 and 32)

Then, a group of elements that are a child of category 33 (in this case 34, 35, and 36)

Then the rest of the "root" categories under category 4 (in this case 37).

So the following query will return the correct results:

SELECT * FROM navigation 
WHERE navigation_store_id = 32 
AND (navigation_category IN (4, 32) 
    OR navigation_path LIKE "4/32/33/%/" 
    OR (navigation_path LIKE "4/%/" 
        AND navigation_category <> 32))

My problem is that I want to order the "groups" of categories in the order listed above (parents of 33 first, children of 33 second, and parents of the root node last). So if they meet the first condition, order them first, if they meet the second condition order them second and if they meet the third (and fourth) condition order them last.

You can see an example of how the category structure works at this site:

www.eanacortes.net

You may notice that it's fairly slow. The current way I am doing this I am using magento's original category table and executing three particularly slow queries on it; then putting the results together in PHP. Using this new table I am solving another issue that I have with magento but would also like to improve my performance at the same time. The best way I see this being accomplished is putting all three queries together and having PHP work less by having the results sorted properly.

Thanks

EDIT

Alright, it works great now. Cut it down from 4 seconds down to 500 MS. Great speed now :)

Here is my code in the Colleciton class:

    function addCategoryFilter($cat)
    {
        $path = $cat->getPath();
        $select = $this->getSelect();
        $id = $cat->getId();
        $root = Mage::app()->getStore()->getRootCategoryId();
        $commaPath = implode(", ", explode("/", $path));

        $where = new Zend_Db_Expr(
            "(navigation_category IN ({$commaPath}) 
                    OR navigation_parent = {$id}
                    OR (navigation_parent = {$root}
                    AND navigation_category <> {$cat->getId()}))");

        $order = new Zend_Db_Expr("
                CASE
                    WHEN navigation_category IN ({$commaPath})  THEN 1
                    WHEN navigation_parent = {$id} THEN 2
                    ELSE 3
                END, LENGTH(navigation_path), navigation_name");

        $select->where($where)->order($order);
        return $this;
    }

Then I consume it with the following code found in my Category block:

        // get our data
        $navigation = Mage::getModel("navigation/navigation")->getCollection();
        $navigation->
            addStoreFilter(Mage::app()->getStore()->getId())->
            addCategoryFilter($currentCat);

        // put it in an array
        $node = &$tree;
        $navArray = array();
        foreach ($navigation as $cat)
        {
            $navArray[] = $cat;
        }
        $navCount = count($navArray);

        $i = 0;

        // skip passed the root category
        for (; $i < $navCount; $i++)
        {
            if ($navArray[$i]->getNavigationCategory() == $root)
            {
                $i++;
                break;
            }
        }

        // add the parents of the current category
        for (; $i < $navCount; $i++)
        {
            $cat = $navArray[$i];

            $node[] = array("cat" => $cat, "children" => array(), 
                "selected" => ($cat->getNavigationCategory() == $currentCat->getId()));
            $node = &$node[0]["children"];

            if ($cat->getNavigationCategory() == $currentCat->getId())
            {
                $i++;
                break;
            }
        }

        // add the children of the current category
        for (; $i < $navCount; $i++)
        {
            $cat = $navArray[$i];
            $path = explode("/", $cat->getNavigationPath());
            if ($path[count($path) - 3] != $currentCat->getId())
            {
                break;
            }

            $node[] = array("cat" => $cat, "children" => array(), 
                "selected" => ($cat->getNavigationCategory() == $currentCat->getId()));
        }

        // add the children of the root category
        for (; $i < $navCount; $i++)
        {
            $cat = $navArray[$i];
            $tree[] = array("cat" => $cat, "children" => array(), 
                "selected" => ($cat->getNavigationCategory() == $currentCat->getId()));
        }

        return $tree;

If I could accept two answers I would accept the first and last one, and if I could accept an answer as "interesting/useful" I would do that with the second. :)

Answer 1

A CASE expression should do the trick.

SELECT * FROM navigation 
    WHERE navigation_store_id = 32 
        AND (navigation_category IN (4, 32) 
            OR navigation_path LIKE "4/32/33/%/" 
            OR (navigation_path LIKE "4/%/" 
            AND navigation_category <> 32))
    ORDER BY
        CASE
            WHEN navigation_category IN (4, 32) THEN 1
            WHEN navigation_path LIKE "4/32/33/%/" THEN 2
            ELSE 3
        END, navigation_path

Answer 2

Try an additional derived column like "weight":

(untested)

(IF(criteriaA,1,0)) + (IF(criteriaB,1,0)) ... AS weight
....
ORDER BY weight 

Each criteria increases the "weight" of the sort. You could also set the weights distinctly by nesting IFs and giving the groups a particular integer to sort by like:

IF(criteriaA,0, IF(criteriaB,1, IF ... )) AS weight

Answer 3

Does MySQL have the UNION SQL keyword for combining queries? Your three queries have mainly non-overlapping criteria, so I suspect it's best to leave them as essentially separate queries, but combine them using UNION or UNION ALL. This will save 2 DB round-trips, and possibly make it easier for MySQL's query planner to "see" the best way to find each set of rows is.

By the way, your strategy of representing the tree by storing paths from root to tip is easy to follow but rather inefficient whenever you need to use a WHERE clause of the form navigation_path like '%XYZ' -- on all DBs I've seen, LIKE conditions must start with a non-wildcard to enable use of an index on that column. (In your example code snippet, you would need such a clause if you didn't already know that the root category was 4 (How did you know that by the way? From a separate, earlier query?))

How often do your categories change? If they don't change often, you can represent your tree using the "nested sets" method, described here, which enables much faster queries on things like "What categories are descendants/ancestors of a given category".