Updating a Mysql column incrementally adding one each time

I had a mysql database that when I add a new value such as 2.5 I wanted to re-order the column with integer numbers (whole). The data column was a decimal(4,1).
Or in other words – a MySQL auto increment but just resetting values back to an even order using PHP.

For example
1.0
2.5
3.0
4.0

Would be renamed like this
1.0
2.0
3.0
4.0

This code will use an sql query to increment a column value by 1.

Use the code as below (change the column names of course!

SET @i:=0;
UPDATE mytable SET mycolumn = @i:=(@i+1) WHERE 1=1 order by mycolumn;