mysql - 如何优化从多个表(到一个表)的删除查询？

Question

好吧，我目前正在从多个表中成功删除，其中三个查询选择了存在category_id的行，除了一个之外，我使用子查询通过category_id获取post_id。如何才能更高效、更全面地做到这一点？谢谢!

/**
 * delete category by id
 * @param $id
 * @return bool
 */
public function delete_category($id){

    $this->db->query("DELETE FROM categories WHERE categories.id = $id");
    $this->db->query("DELETE FROM comments
                      WHERE comments.post_id = ANY (SELECT post_id
                                                    FROM posts
                                                    WHERE category_id = $id)");
    $this->db->query("DELETE FROM posts
                      WHERE posts.category_id = $id
                      AND posts.category_id IS NOT NULL");
}

代码工作正常，给出了期望的结果，但看起来有点恶心，我该如何优化它？

Answer 1

MySQL有一个multi-table DELETE syntax .

您实际上采用一个 SELECT 查询来选择要删除的行，然后更改 SELECT * FROM至DELETE <table_name>, <table_name> FROM ，与 <table_name>, <table_name>是要从中删除的表。

例如，如果您有以下 DELETE 查询:

DELETE FROM comments WHERE post_id IN (SELECT post_id FROM posts WHERE category_id = 1);
DELETE FROM posts WHERE category_id = 1;
DELETE FROM categories WHERE category_id = 1;

您可以将它们重写为选择要删除的所有行的 SELECT:

SELECT *
FROM categories
JOIN posts USING (category_id)
JOIN comments USING (post_id)
WHERE category_id = 1

然后你可以替换 SELECT与多表DELETE :

DELETE categories, posts, comments
FROM categories
JOIN posts USING (category_id)
JOIN comments USING (post_id)
WHERE category_id = 1