Question

我有四个桌子。首先，让我分享他们的结构

子类别

id
name

子类别三

id
name
sub_category_id

产品

id
name
sub_category_three_id

图片

 id
 image
 product_id

现在，我想获得1个sub_category，并在sub_category（id）的基础上获取来自子类别3的所有数据，并在sub_category_three的基础上获取sub_category_three的所有产品，并在产品基础上获取所有图像。

我在三个表上尝试了该查询，但是随后变得很复杂，所以我来到了这里。

SELECT sct.sct_name,sc_name,p.name 
  FROM sub_categories_three sct 
 INNER JOIN sub_categories sc 
    ON sc.id = sct.sub_category_id 
 INNER JOIN products p 
    ON sct.id = p.sub_category_three

Answer 1

这是一个简单的联接查询，用于连接所有表：

select * from sub_category sc inner join
  sub_category_three sct on sc.id = sct.sub_category_id inner join
  products p on sct.id = p.sub_category_three_id inner join 
  images i on i.product_id = p.id
  where ....

Answer 2

这是简单的内部联接查询

SELECT * FROM products 
INNER JOIN images ON images.product_id = products.id                           //link images with product id 
INNER JOIN sub category three sct ON sct.id = products.subcategory_three_id    //link product subcategory three id with sub category three 
INNER JOIN sub category sc ON sc.id = sct.sub_category_id                     //finally link sub category with subcategory three `

如有必要，添加条件

编辑

SELECT * FROM products 
INNER JOIN images ON images.product_id = products.id                           //link images with product id 
INNER JOIN sub category three sct ON sct.id = products.subcategory_three_id    //link product subcategory three id with sub category three 
INNER JOIN sub category sc ON sc.id = 
  (  SELECT id
       FROM sub category AS sc
        WHERE sc.id = sct.sub_category_id
        LIMIT 1

   )             //finally link sub category with subcategory three `

Answer 3

您可以使用以下查询，其中包含一些说明：

exp(X)

希望如此，请随时提出更多说明。

使用一个信号查询从四个表中获取数据

3 个答案: