MYSQL查询没有返回正确的行集

Question

我有两张桌子：

table_subcategories - sub_categories_id, sub_category_name, sub_category_image_path
table_subcategory_categories - subcategory_id, category_id

我想从table_subcategories获取所有子类别，其中没有映射条目存在于＆＃34; table_subcategory_categories＆＃34;给定category_id

我正在使用此查询，但结果不正确。

my $sql_query = "SELECT  TSC.sub_categories_id, TSC.sub_category_name, TSC.sub_category_image_path  from table_subcategories as TSC 
INNER JOIN
table_subcategory_categories as TSCC
ON
TSC.sub_categories_id = TSCC.subcategory_id
WHERE
TSCC.category_id != $cId ";

可以请一些人帮我解决这个问题吗？

Answer 1

使用left join并检查不匹配：

SELECT TSC.* 
from table_subcategories TSC LEFT JOIN
     table_subcategory_categories  TSCC
     ON TSC.sub_categories_id = TSCC.subcategory_id AND
        TSCC.Category_Id = $cId
WHERE TSCC.category_id IS NULL;