具有多个搜索参数的内部联接意外返回空

Question

汽车

身份证	名字	型号	年份
1	大众高尔夫	1121	2010
2	闪避	3234	2016
3	奥迪	5335	2394
4	宝马	6567	9090
5	丰田	1221	9090

汽车功能

身份证	特点
1	货叉厚度
2	操作员保护
3	后轮胎

汽车规格

身份证	车号	价值	汽车功能 ID
1	1	1.50	1
2	1	开放式开销	2
3	1	夏季轮胎	3
4	2	1.30	1
5	2	封闭式架空	2
6	2	冬季轮胎	3
7	3	1.20	1
8	3	封闭式架空	2
9	3	冬季轮胎	3

这将返回汽车

where Feature.Feature = 'ForkThickness' and corresponding CarSpec.Value > 1.25

--汽车 1 和 2 的 carId 和汽车名称。

SELECT DISTINCT ca.Id, ca.Name 
FROM Car AS ca
INNER JOIN CarSpec AS cs
    ON ca.id = cs.CarId    
INNER JOIN CarFeature AS cf
    ON cf.Id = cs.CarFeatureId    
WHERE cf.Feature = 'ForkThickness' AND cs.Value > 1.25

在搜索参数中包含更多功能应该只返回汽车 1，但它返回空：

WHERE Feature.Feature = 'ForkThickness' AND CarSpec.Value > 1.25
AND Feature.Feature = 'RearTires' AND CarSpec.Value = 'Summer Tires'

我做错了什么？

Answer 1

您可以使用

GROUP BY ... HAVING

和条件聚合来断言多个条件。 小提琴

SELECT ca.Id,
       ca.Name 
FROM   Car AS ca
WHERE  ca.Id IN (SELECT cs.CarId
                 FROM   CarSpec AS cs
                        INNER JOIN CarFeature AS cf
                                ON cf.Id = cs.CarFeatureId
                 GROUP  BY cs.CarId
                 HAVING 1 = MAX(IIF(( cf.Feature = 'ForkThickness' AND TRY_CAST(cs.Value AS DECIMAL(10, 2)) > 1.25 ), 1, 0))
                        AND 1 = MAX(IIF(( cf.Feature = 'RearTires' AND cs.Value = 'Summer Tires' ), 1, 0))) 

Answer 2

您尝试的问题是您正在添加更多连接条件，因此您正在寻找具有这两个条件的单个规范/功能。而实际上您想分别检查每个条件。有很多方法可以做到这一点，但

EXISTS

是我的选择，因为它在逻辑上代表了您想要完成的任务。

SELECT ca.Id, ca.Name 
FROM Car c
WHERE EXISTS (
    SELECT 1
    FROM CarSpec cs
    JOIN CarFeature cf on cf.Id = cs.CarFeatureid
    WHERE cs.CarId = c.Id
    AND cf.Feature = 'ForkThickness' AND cs.Value > 1.25
);

还有

SELECT ca.Id, ca.Name 
FROM Car c
WHERE EXISTS (
    SELECT 1
    FROM CarSpec cs
    JOIN CarFeature cf on cf.Id = cs.CarFeatureid
    WHERE cs.CarId = c.Id
    AND cf.Feature = 'ForkThickness' AND cs.Value > 1.25
)
AND EXISTS (
    SELECT 1
    FROM CarSpec cs
    JOIN CarFeature cf on cf.Id = cs.CarFeatureid
    WHERE cs.CarId = c.Id
    AND cf.Feature = 'RearTires' AND cs.Value = 'Summer Tires'
);

Answer 3

您可以将具有不同条件的查询分开，然后将它们合并在一起

SELECT ca.Id, ca.Name 
FROM 
   Car AS ca 
   INNER JOIN CarSpec AS cs ON ca.id = cs.CarId    
   INNER JOIN CarFeature AS cf ON cf.Id = cs.CarFeatureId    
WHERE cf.Feature = 'ForkThickness' AND cs.Value > 1.25
    
UNION

SELECT ca.Id, ca.Name 
FROM 
   Car AS ca 
   INNER JOIN CarSpec AS cs ON ca.id = cs.CarId    
   INNER JOIN CarFeature AS cf ON cf.Id = cs.CarFeatureId    
WHERE cf.Feature = 'RearTires' AND cs.Value = 'Summer Tires'

UNION 默认会删除所有重复项

Answer 4

您的代码正在寻找同时具有Feature.Feature = ForkThickness AND Feature.Feature = RearTires 的东西。

WHERE Feature.Feature = 'ForkThickness' AND CarSpec.Value > 1.25
AND Feature.Feature = 'RearTires' AND CarSpec.Value = 'Summer Tires'

这可以与 OR 语句一起使用来查找选项，否则您可以删除双“Feature.Feature”参数/要求。

相反，将 AND 语句替换为 OR 语句：

WHERE (Feature.Feature = 'ForkThickness' AND CarSpec.Value > 1.25)
OR (Feature.Feature = 'RearTires' AND CarSpec.Value = 'Summer Tires')

这将导致找到 2 辆车。

或者，如果您希望获得 1 个结果，您可以使用以下内容。 但只需检查您的逻辑，具体取决于您的实际需求。

WHERE (Feature.Feature = 'ForkThickness' OR Feature.Feature = 
'RearTires') AND CarSpec.Value > 1.25 AND CarSpec.Value = 'Summer Tires'