如何正确匹配左联接？

Question

I'm trying to properly match a left-join, where you delete filter and information pieces that are recorded in X table for this filter.

Here is my example:

table d_category

filter_id
7
8

table d_name

id | filter_id
10 | 7
11 | 7
12 | 7

table product_d

product_id | d_name_id
50         | 10
50         | 11
50         | 12

The Query

$this->db->query("DELETE FROM product_d
LEFT JOIN d_name ON (product_d.d_name_id = d_name.id) 
WHERE"); // what should this clause be?

Answer 1

I assume that you are looking for Cascading Delete . If that is the case:

If you configure your Foreign Keys to have cascade delete , all related data will also get deleted when you delete record from parent table.

CREATE TABLE rooms (
    room_no INT PRIMARY KEY AUTO_INCREMENT,
    room_name VARCHAR(255) NOT NULL,
    building_no INT NOT NULL,
    FOREIGN KEY (building_no)
        REFERENCES buildings (building_no)
        ON DELETE CASCADE
);

then when you delete building, rooms also get deleted

DELETE FROM buildings 
WHERE
  building_no = 2;