SqlServer:

SELECT LFGJA*100+LFMON as "期间",MATNR as "品号",(CASE WHEN ISNULL(PEINH,0)=0 THEN NULL ELSE VERPR/PEINH END) as "实际成本",STPRS/PEINH  as "标准成本"

FROM "SAPABAP1"."MBEWH"

where 1=1  ${if(len(期间) == 0,""," and LFGJA*100+LFMON = '" + 期间 + "'")}  and BWKEY = '1012' 

ORACLE:

SELECT LFGJA*100+LFMON as "期间",MATNR as "品号",(CASE WHEN NVL(PEINH,0)=0 THEN NULL ELSE VERPR/PEINH END) as "实际成本",STPRS/PEINH  as "标准成本"

FROM "SAPABAP1"."MBEWH"

where 1=1  ${if(len(期间) == 0,""," and LFGJA*100+LFMON = '" + 期间 + "'")}  and BWKEY = '1012' 

MYSQL

SELECT LFGJA*100+LFMON as "期间",MATNR as "品号",(CASE WHEN IFNULL(PEINH,0)=0 THEN NULL ELSE VERPR/PEINH END) as "实际成本",STPRS/PEINH  as "标准成本"

FROM "SAPABAP1"."MBEWH"

where 1=1  ${if(len(期间) == 0,""," and LFGJA*100+LFMON = '" + 期间 + "'")}  and BWKEY = '1012' 

看一下有没有分母为零的数据，分母最好做个为0判断

你是什么数据库？你看一下你的数据格式。里面是不是有空格的行，或者其它不可见的字符，或者是文本的，还有如果不相除的话，只写字段是否报错，把明细拉出来看