我需要显示来自 BRAND_CAR 的所有汽车，即使其中没​​有汽车

Question

我创建了这个查询，即使在车辆表上创建了 0 个车辆，我也无法显示所有品牌汽车。

SELECT BRAND_CAR_NAME, COUNT(*)
FROM brand b, vehicule v, model mo
WHERE v.ID_MODEL = mo.ID_MODEL
AND mo.ID_BRAND = b.ID_BRAND
GROUP BY BRAND_CAR_NAME

它告诉我什么：

Brand 1 :   1
Brand 3 :   1 
Brand 4 :   1
Brand 6 :   1

我想看看：

            Brand 1 : 1
            Brand 3 : 1 
            Brand 4 : 1
            Brand 6 : 1
            brand 2 : 0
            brand 5 : 0
            brand 7 : 0

SELECT NOM_MARQUE, IFNULL(v.ID_VOITURE)
FROM marque m, voiture v, model mo
WHERE v.ID_MODEL = mo.ID_MODEL
AND mo.ID_MARQUE = m.ID_MARQUE
GROUP BY NOM_MARQUE

Answer 1

使用Left Join得到结果，试试下面的查询

SELECT b.BRAND_CAR_NAME, COUNT(*) 
FROM brand b
LEFT JOIN model mo ON b.ID_BRAND = mo.ID_BRAND
INNER JOIN vehicule v ON mo.ID_MODEL = v.ID_MODEL
GROUP BY b.BRAND_CAR_NAME;

Answer 2

您可以使用LEFT JOIN，尤其是在vehicule 表和SUM( IFNULL(SIGN(v.ID_MODEL),0) ) 之前

（我认为在model 表之前使用LEFT JOIN 更好，因为model 表缺少记录）

SELECT BRAND_CAR_NAME, SUM( IFNULL(SIGN(v.ID_MODEL),0) ) as BRAND_COUNT
  FROM brand b
  LEFT JOIN model mo ON mo.ID_BRAND = b.ID_BRAND
  LEFT JOIN vehicule v ON v.ID_MODEL = mo.ID_MODEL
 GROUP BY BRAND_CAR_NAME;

Demo