带有多个INNER JOIN的MySQL ORDER BY

Question

I can't seem to figure out how to order by in this MySQL select. I hope you can help me out.

Tabels:

categories

catId, catParentId, catDisplay
1      0            1
2      0            1
3      0            1
4      1            1
5      1            1

categories_translation

transId, catId, catName, catDesc, langId
1        1      Title1   Desc1    1
2        2      Title2   Desc2    1
3        3      Title3   Desc3    1
4        4      Title4   Desc4    1
5        5      Title5   Desc5    1

language

langId, langName, langCode
1       Danish    da
2       English   en

My query:

SELECT `categories`.`catId`,
       `categories`.`catParentId`,
       `categories`.`catDisplay`,
       `categories_translation`.`catName`,
       `categories_translation`.`catDesc`,
       `language`.`langCode`
FROM   `categories`
INNER JOIN `categories_translation` ON `categories_translation`.`catId` = `categories`.`catId`
INNER JOIN `language` ON `language`.`langId` = `categories_translation`.`langId`
WHERE `language`.`langCode` = 'da'

Now, I get returned what I want, but is there a way to order the child categories to their parents, so the result looks like this:

Desired result:

catId | catParentId | catDisplay | catName | catDesc | langCode
1       0             1            Title1    Desc1     da
4       1             1            Title4    Desc4     da
5       1             1            Title5    Desc5     da
2       0             1            Title2    Desc2     da
3       0             1            Title3    Desc3     da

I've tried order by, but can seem to get the results like I want.

Answer 1

Try the following:

ORDER BY
    CASE WHEN categories.catParentId = 0 THEN
        categories.catId
    ELSE 
        categories.catParentId
    END,
    CASE WHEN categories.catParentId = 0 THEN
        0
    ELSE
        categories.catId
    END

For those that don't get the ordering it would be easier to think of the desired result as:

catId | catParentId | orderingCategory
1       0             1.0
4       1             1.4
5       1             1.5
2       0             2.0
3       0             3.0

So it's a hierarchy of categories, OP wants to order the result so that each parent categories are followed by their child categories.