[mallen]

I have this query that works and displays a list of categories. But I need to combine the products table into it. This is to only list categories that have products with a value of "1". Not sure how to include a second LEFT JOIN. My products table is prod_id, company_abc and I need to include WHERE company_abc = '1'

SELECT 
        main_categories.cat_id AS main_cat_id
        , main_categories.cat_name AS main_cat_name
        , child_categories.cat_id AS child_cat_id
        , child_categories.cat_name AS child_cat_name
        FROM
        categories AS main_categories
        LEFT JOIN categories AS child_categories
        ON child_categories.cat_parent = main_categories.cat_id
        WHERE main_categories.cat_parent IS NULL
        ORDER BY
        main_categories.cat_name ASC 

[MrFujin]

You add the second LEFT JOIN similar to the first one.
something like this:

...
LEFT JOIN categories AS child_categories
        ON child_categories.cat_parent = main_categories.cat_id
LEFT JOIN products AS products
        ON products.prod_id = main_categories.prod_id AND products.value = 1
WHERE main_categories.cat_parent IS NULL 
..

You have to modify it with the correct table names and conditions.

[mallen]

Thanks I tried it and changed the table names.

        SELECT main_categories.cat_id AS main_cat_id
        , main_categories.cat_name AS main_cat_name
        , child_categories.cat_id AS child_cat_id
        , child_categories.cat_name AS child_cat_name
        FROM categories AS main_categories
        LEFT JOIN categories AS child_categories
        LEFT JOIN products AS products ON products.prod_id = main_categories.prod_id
    AND `company_abc` = '1'
    WHERE main_categories.cat_parent IS NULL 

I get an error: "You have an error ...WHERE main_categories.cat_parent IS NULL LIMIT 0, 50' at line 10"

[Jacques1]

You can't have a LEFT JOIN without a condition. This simply makes no sense. Interestingly, you did have it in your original query, and MrFujin also included it, but then somehow it got lost.

And if the AND part is supposed to belong to the WHERE clause, it has to actually be there and not before it. Currently, it belongs to the join condition.

[mallen]

Thanks I didn't catch that I left off that line. Not getting any errors but it is not factoring in the products table. Shouldn't list categories that don't have "1" for company_abc.
Also its returning only 28 of 50 categories.

SELECT main_categories.cat_id AS main_cat_id
        , main_categories.cat_name AS main_cat_name
        , child_categories.cat_id AS child_cat_id
        , child_categories.cat_name AS child_cat_name
        FROM categories AS main_categories
        LEFT JOIN categories AS child_categories
        ON child_categories.cat_parent = main_categories.cat_id
        LEFT JOIN products AS products ON products.prod_id = main_categories.cat_id
        WHERE `company_abc` = '1'
        AND main_categories.cat_parent IS NULL
        ORDER BY main_categories.cat_name ASC 

[Jacques1]

Originally Posted by mallen

Shouldn't list categories that don't have "1" for company_abc.

Your join condition says

products.prod_id = main_categories.cat_id

I'm pretty sure that's not what you want.

Originally Posted by mallen

Also its returning only 28 of 50 categories.

Apart from the problem above: The query will reject all categories without products, because you require company_abc to be 1. Is that what you want? Then remove the "LEFT" from LEFT JOIN products. You're effectlively doing an inner join, because all additional rows caused by the left join are immediately removed due to the company_abc = 1 check. So there's no reason to pretend you're doing a left join. If you do want a left join, then you need to allow company_abc IS NULL as well.

[mallen]

Thanks. I changed it to
= main_categories.prod_id
also changed LEFT JOIN to INNER JOIN Now it doesn't return any categories.

main_categories.cat_id AS main_cat_id
        , main_categories.cat_name AS main_cat_name
        , child_categories.cat_id AS child_cat_id
        , child_categories.cat_name AS child_cat_name
        FROM categories AS main_categories
        LEFT JOIN categories AS child_categories
        ON child_categories.cat_parent = main_categories.cat_id
        INNER JOIN products AS products ON products.prod_id = main_categories.prod_id
        WHERE `company_abc` = '1'
        AND main_categories.cat_parent IS NULL
        ORDER BY main_categories.cat_name ASC 

[Jacques1]

A category has exactly one product? That doesn't make a lot of sense to me. Or is this some kind of special product? Then you should actually make that clear in the name (call it something like "top_product" or so).

Anyway, the great thing about SQL (or tech stuff in general) is that everything happens for a reason. You can actually investigate problems. Do that. Don't wait for us to debug your queries.

For example, an obvious step would be to join the categories with the products and see if there are in fact categories with company_abc = 1.

SELECT
	main_categories.cat_id
	, products.company_abc
FROM
	categories AS main_categories
	JOIN
		products ON products.prod_id = main_categories.prod_id	-- really?
WHERE
		main_categories.cat_parent IS NULL
ORDER BY
	products.company_abc = 1 DESC
;

Do you actually see results with the company 1?

By the way, please remove those backtick leftovers from company_abc. You should qualify that name (write a table prefix before it) so that it's clear where it comes from.

Aliasing a table with the same name ("products AS products") doesn't make a lot of sense either.

[r937]

Originally Posted by Jacques1

Anyway, the great thing about SQL (or tech stuff in general) is that everything happens for a reason.

this is what i like about sql too (but i have also felt the frustration, the exasperation, the befuddlementation that sql bestows, so i try to be kind to noobs)

the best explanations are the simplest

wait'll you tell him where company_abc = 1 needs to go in a left outer join

[MrFujin]

Originally Posted by Jacques1

Aliasing a table with the same name ("products AS products") doesn't make a lot of sense either.

That alias was a mistake from my part.

@mallen

As Jacques1 implies, you should probably not join the products with main_categories.
Have you tried to join the products with child_categories?

Originally Posted by r937

wait'll you tell him where company_abc = 1 needs to go in a left outer join

Just me who can't understand the meaning of this?

[r937]

Originally Posted by MrFujin

Just me who can't understand the meaning of this?

okay, let me explain briefsly

maincat-LEFT-categ-LEFT-products implies you want the category tree and any products tied to the 2nd level if any

putting a condition on a products column into the WHERE clause makes the sql behave like an inner join, not an outer join

putting that condition into the ON clause of the outer join means you still get the entire category tree

[mallen]

WHERE `company_abc` = '1' is part of my query I have used before. I know, I know bad design but someone else did it and I am leaving it for now. I have many products for each company. I have a working query that displays all the categories, sub categories, and products. I also have a working query that only lists main categories but leaves out "this company =1" and the products table. Incorporating this line is what I am have hard time with.
This first one works, and there are no sub categories to display.

SELECT cat.cat_name, cat.cat_id FROM categories as cat
                        LEFT JOIN category_assoc as assoc
                        ON assoc.cat_id = cat.cat_id
                        LEFT JOIN products as pr
                        ON pr.prod_id = assoc.prod_id
                        WHERE `". $this->company . "` = '1'
                        ORDER BY cat.cat_name ASC"; 

This one almost most works but displays categories that have no products associated with them. I don't want any categories to be listed if there are no products.

SELECT 
        main_categories.cat_id AS main_cat_id
        , main_categories.cat_name AS main_cat_name
        , child_categories.cat_id AS child_cat_id
        , child_categories.cat_name AS child_cat_name
        FROM
        categories AS main_categories
        LEFT JOIN categories AS child_categories
        ON child_categories.cat_parent = main_categories.cat_id
        WHERE main_categories.cat_parent IS NULL
        ORDER BY
        main_categories.cat_name ASC 

Upon further thought, I changed the categories that don't have products from NULL to "0" on the cat_parent table and now they don't show. The condition for the company being "1" is what determines the list of categories. So each of the companies don't have the same list.

[mallen]

I solved it.

SELECT DISTINCT
    main_categories.cat_id AS main_cat_id
    , main_categories.cat_name AS main_cat_name
    , child_categories.cat_id AS child_cat_id
    , child_categories.cat_name AS child_cat_name
    FROM categories AS main_categories
    LEFT JOIN categories AS child_categories
    ON child_categories.cat_parent = main_categories.cat_id
    LEFT JOIN category_assoc AS assoc
    ON assoc.cat_id = main_categories.cat_id
    LEFT JOIN products AS pr
    ON pr.prod_id = assoc.prod_id
    WHERE main_categories.cat_parent IS NULL
    AND `". $this->company . "` = '1'
    ORDER BY
    main_categories.cat_name ASC 

[r937]

Originally Posted by mallen

I solved it.

if `". $this->company . "` represents a column in the products table, then you haven't understood how LEFT OUTER JOINs work

change them all to INNER JOINs