Updating display order of multiple MySQL rows in one or very few queries

Question

I have a table with say 20 rows each with a number for display order (1-20).

SELECT * FROM `mytable` ORDER BY `display_order` DESC;

From an adm

Answer 1

I'm thinking about this problem, and the solution I came up is having a decimal number as order and change the number of the item change for a number between the next and the previous item

Order    Item
-----    ----
1        Original Item 1
2        Original Item 2
3        Original Item 3
4        Original Item 4
5        Original Item 5

If you change the item 4 to the 2nd position, you get:

Order    Item
-----    ----
1        Original Item 1
1.5      Original Item 4
2        Original Item 2
3        Original Item 3
5        Original Item 5

If you change the item 3 to the 3rd position, you get:

Order    Item
-----    ----
1        Original Item 1
1.5      Original Item 4
1.75     Original Item 3
2        Original Item 2
5        Original Item 5

Theoretically there is always a decimal between two decimals, but you could face some storage limits.

This way you only have to update the row being re-ordered.