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如何删除没有产品的类别?

[英]How to remove categories with no products?

I am a bit stuck on the following SQL: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);

It removes all data ignoring the where part.它删除所有数据而忽略where部分。 What am I doing wrong?我究竟做错了什么?

You need to remove the single quotes around the column name, otherwise it becomes a literal string, and the expression does not do what you want.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。 It actually checks if literal string 'category_id' belongs to the resulset of the subquery: since it probably does not, all rows get deleted.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。

Also, I would recommend using exists , which is null -safe, while not in is not (that is, if any value in the subquery is null , all rows will be deleted).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
);

For performance, consider an index on oc_product_to_category(category_id) (or at least a compound index where this column appears first).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)。

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