SELECT *,
SUM( `Janunits` + `Febunits` + `Marunits` + `Aprunits` + `Mayunits` + `Jununits` + `Julunits` + `Augunits` + `Sepunits` + `Octunits` + `Novunits` + `Decunits` ) AS TotalUnits,
IF(`TotalUnits`=0,0,SUM ( `TotalUnits` - `inventory.Year1qty` ) / `TotalUnits`) AS Percent
FROM `inventory`
WHERE `Dept` = 'WIDGETS'
GROUP BY Item