Question

I hope some one more SQL wise can help me. Suppose the following table and relationships they’re compacted.

orders(PK_refno,customer, status)
order_accessories(PK_refno,PK_acc)
accessories(PK_acc,name,desc)

As you can see this is a typical 1:*----*:*----*:1 scenario the the issue or my concern is when updating, as the accessories that each order has can be modified, meaning that an user can add/remove accessories.

The only way I’ve thought to do it by using MySQL is to delete all accessories and then insert the updated ones.

I dislike it this way. As I think that probably there’s a SQL way to do it. Maybe someone can suggest and advanced query (which I’ll study of course)

The other way I thought was to:

Retrieve the originals.

Compare them and remove/add the differences.

I’m not a fan of this either because it would be done in the app, not in the database.

Answer 1

Let’s say the table starts like this.

order_accessories
PK_refno  PK_acc
1         73
1         74
1         75
1         86
1         92

Let’s also say that 75 is supposed to be 76. Assuming a sane user interface, the user can just change 75 to 76. A sane user interface would send this statement to the dbms.

update order_accessories
set PK_acc = 76
where (PK_refno = 1 and PK_acc = 75);

If 75 were not supposed to be there in the first place, then the user would just delete that one row. A sane user interface would send this statement to the dbms.

delete from order_accessories
where (PK_refno = 1 and PK_acc = 75);