当删除同一表中的另一行时，将行内的部分/全部值更新为null

Question

I have a mysql table like below

id  tetangga1 tetangga2
1   null     null                       
2   1        3              
3   1        4           
4   4        5         
5   4        6         
6   6        null      

i need to update either tetangga row's value to NULL when one of the row inside the same table is deleted, in example, if i delete the row 1, then the table would look like this

id  tetangga1 tetangga2                       
2   NULL        3              
3   NULL        4           
4   4           5         
5   4           6         
6   6           NULL  

explanation: row 1 will be deleted, row 2 and 3 tetangga1's value will be updated to null

how can i achieve it?

Answer 1

You can do this with a foreign key relationship defined appropriately:

alter table t
    add constraint fk_t_tetangga1
        foreign key (tetangga1) references t(id)
        on delete set NULL;

This is actually better than a trigger. The database will maintain the relational integrity.