MySQL查询没有得到期望的结果

Question

I am trying to get all the "afdelingen" which are 2 and the name of the "directeur" behind the "afdelingen.naam" base on his "functienaam". But I only get the "afdelingen.naam" with the name of the "Directeur".

How do I also get the other "afdelingen.naam" in this result.

This is what I currently have:

SELECT afdelingen.naam, personeel.voornamen, personeel.tussenvoegsels, personeel.achternaam, rollen.functienaam
FROM `afdelingen` INNER JOIN
     personeel_afdeling
     ON afdelingen.id = personeel_afdeling.afdeling_id INNER JOIN 
     personeel
     ON personeel_afdeling.personeel_id = personeel.id INNER JOIN
     rollen
     ON personeel_afdeling.rol_id = rollen.id
WHERE rollen.id LIKE 1

Current result: Disign & Ontwikkeling | Wilhelmus Frederikus Aloisius | van | Hot naar Her | Directeur

Desired result:

• Verkoop & Administratief
• Disign & Ontwikkeling | Wilhelmus Frederikus Aloisius | van | Hot naar Her | Directeur

Answer 1

Left joins as mentioned by @rickdenhaan are only part of it; you're also filtering for rollen.id = 1 . Since the "Verkoop & Administratief" afdeling (I think that's the right singular?) does not have a Directeur, you're eliminating that row from your result set with the WHERE clause.

Instead of filtering with a WHERE , add the filter to your join condition so you only join the Directeur role. And use LEFT JOIN s to ensure that you join nothing if there is no Directeur instead of removing rows from your dataset without the corresponding role.