Use a floating point number for the position column.

You can then reorder the list changing only the position column in the "moved" row.

Basically if your user wants to position "red" after "blue" but before "yellow"

Then you just need to calculate

red.position = ((yellow.position - blue.position) / 2) + blue.position 

After a few million re-positions you may get floating point numbers so small that there is no "between" -- but this is about as likely as sighting a unicorn.

Use a floating point number for the position column.

You can then reorder the list changing only the position column in the "moved" row.

Basically if your user wants to position "red" after "blue" but before "yellow"

Then you just need to calculate

red.position = ((yellow.position - blue.position) / 2) + blue.position 

After a few million re-positions you may get floating point numbers so small that there is no "between" -- but this is about as likely as sighting a unicorn.

You could implement this using an integer field with an initial gap of say 1000. So your intial oredring would be 1000->blue,2000->Yellow,3000->Red. After "moving" Red after blue you would have 1000->blue,1500->Red,2000->Yellow.

The problem is that with a seemingly large initial gap of 1000 as few as 10 moves will get you into a situation like 1000->blue,1001-puce,1004->biege ...... where you will no longer be able to insert anything after "blue" without re-number the whole list. Using floating point numbers there will always be a "halfway" point between the two positions.