如何删除没有产品的类别？

Question

我有点卡在以下 SQL 上：

delete  from oc_category_description where 'category_id' NOT in (SELECT category_id FROM oc_product_to_category);
delete from oc_category_path where 'category_id' NOT in(SELECT category_id from oc_product_to_category);
delete from oc_category_to_store where 'category_id' NOT in(SELECT category_id from oc_product_to_category);
delete from oc_category_to_layout where 'category_id' NOT in(SELECT category_id from oc_product_to_category);
delete from oc_category_filter where 'category_id' NOT in(SELECT category_id from oc_product_to_category);
delete from oc_coupon_category where 'category_id' NOT in(SELECT category_id from oc_product_to_category);
delete from oc_category where 'category_id' NOT in(SELECT category_id from oc_product_to_category);

它删除所有数据而忽略where部分。 我究竟做错了什么？

Answer 1

您需要删除列名周围的单引号，否则它会变成文字字符串，并且表达式不会执行您想要的操作。 它实际上检查文字字符串'category_id'是否属于子查询的结果集：因为它可能不属于，所以所有行都被删除。

另外，我建议使用exists ，即null ，而not in则不是（也就是说，如果子查询中的任何值为null ，则所有行都将被删除）。

delete from oc_category 
where not exists (
    select 1 
    from oc_product_to_category pc 
    where pc.category_id = oc_category.category_id
);

为了提高性能，请考虑oc_product_to_category(category_id)上的索引（或至少是此列首先出现的复合索引）。