sqlite query do simple calculations on result of subquery
You need to use a subquery, because a column alias cannot be re-used at the same level of select:
SELECT t.*, ((summeJ-summeVJ)/summeVJ*100) AS varianceFROM (SELECT k.ZKUNDENNR, k.ZNAME1, (SELECT SUM(vk.ZNETTO) FROM ZPBSROW r LEFT JOIN ZWARENGRUPPEVK vk ON vk.ZPBSROW=r.Z_PK WHERE r.ZKUNDE=k.Z_PK AND ZJAHR=2013 AND ZMONAT>=1 AND ZMONAT<=6) AS summeJ, (SELECT SUM(vk.ZNETTO) FROM ZPBSROW r LEFT JOIN ZWARENGRUPPEVK vk ON vk.ZPBSROW=r.Z_PK WHERE r.ZKUNDE=k.Z_PK AND ZJAHR=2012 AND ZMONAT>=1 AND ZMONAT<=6) as summeVJ, (SELECT SUM(vk.ZDB_BASIS) FROM ZPBSROW r LEFT JOIN ZWARENGRUPPEVK vk ON vk.ZPBSROW=r.Z_PK WHERE r.ZKUNDE=k.Z_PK AND ZJAHR=2012 AND ZMONAT>=1 AND ZMONAT<=6) as summeDBVJ, (SELECT SUM(vk.ZDB_BASIS) FROM ZPBSROW r LEFT JOIN ZWARENGRUPPEVK vk ON vk.ZPBSROW=r.Z_PK WHERE r.ZKUNDE=k.Z_PK AND ZJAHR=2013 AND ZMONAT>=1 AND ZMONAT<=6) as summeDBJ FROM ZKUNDE k ) tWHERE summeJ>0ORDER BY summeJ DESCLIMIT 0,10