I am developing a web application which will have images displayed in a slider. It is important that I am able to modify the order that they are displayed in.
Currently, I have a column in the table of images called 'order', which must be set to ensure the ordering works correctly, but changing it requires changing every other, too, which becomes tricky when dealing with hundreds of records.
This table, as well as queries for modifying it, are in development, so it's completely fine to change the way I do this.
My questions are:
Query the table you are about to insert into to find the MAX id in the table. Then on your insert just do this +1.
When re-ordering, say you want to set image order 6 to order 3. You will want to update all rows from order 3 and onwards to order+1 then set the image to order 3.
UPDATE table SET id = id+1 WHERE id IN (SELECT * FROM table where id >= 3)
You could on delete of a picture re-evaluate the ids to keep no gaps
UPDATE table SET id = id-1 WHERE id IN (SELECT * from TABLE WHERE id > 3)
Where 3 is the deleted id