Question

我有3个表，我想运行查询，我想要做的是如下：

SELECT table1.name AS product_name,
            table1.description AS product_description,
            table2.name AS product_category
            table3.product_id
            FROM table1
            INNER JOIN table1 a ON table3.product_id = table1.product_id
            INNER JOIN  table2 b ON table3.category_id = table2.category_id
            INNER JOIN table2 ON table1.product_id = table2.product_id;

TABLE2和TABLE1之间的链接是product_ID和category_ID，它们都在TABLE3上

所以这是我试图运行的查询

{{1}}

表的结构如下：表1（产品编号，名称，描述）表2（CATEGORY_ID，名2）表3（product_id，category_id）

Answer 1

如果您使用assign alias（table1 a，表2b）到表，则使用它，否则不指定。您正在加入两个时间表2而不是表3，并假设table2和table1通过category_id相关联和table3 table1通过product_id和category_id

相关联

  SELECT 
       table1.name AS product_name
      ,table1.description AS product_description
      ,table2.name AS product_category
      ,table3.product_id
  FROM table1
  INNER JOIN table2  table1.category_id = table2.category_id ;
  INNER JOIN table3  ON table3.product_id = table1.product_id  
          and table3.category_id = table1.category_id

Answer 2

Table1.category_id = Table2.category_id 的条件在哪里？

无法让sql表加入工作

2 个答案: