SQL问题，有警告: 聚合或其他 SET 操作消除了空值

[why0826002]

SELECT cast(sum(A.sl) as int) as 入库箱数,CAST(sum(B.sl) AS INT) AS 出库箱数,cast(sum(A.sl) as int)-CAST(sum(B.sl) AS INT) as 理论库存箱数 from
(select distinct sl,barcode from bjdata.dbo.informationdata where users<>'out-1') as A
left join
(select distinct sl,barcode from bjdata.dbo.informationdata where users='out-1') AS B
on LEFT(A.barcode,len(A.barcode)-8)=left(B.barcode,len(B.barcode)-8)


在语句中进行了左连接，有的产品有可能入库中有，而出库中没有，这样连接完之后，就会有这样的结果，
执行完的结果为
入库箱数 出库箱数 理论库存箱数
39 NULL NULL

请问怎么将出库箱数和理论库存箱数,若为NULL，则显示为0，若不为空，则显示为真实的数字.

这个应该怎么实现呢？

[王向飞]

SELECT cast(sum(A.sl) as int) as 入库箱数,
isnull(CAST(sum(B.sl) AS INT),0) AS 出库箱数,
isnull(cast(sum(A.sl) as int)-CAST(sum(B.sl) AS INT),0) as 理论库存箱数 
from  
(select distinct sl,barcode from bjdata.dbo.informationdata where users<>'out-1') as A
left join
(select distinct sl,barcode from bjdata.dbo.informationdata where users='out-1') AS B
on LEFT(A.barcode,len(A.barcode)-8)=left(B.barcode,len(B.barcode)-8)

[claro]

ISNULL

[xiaoxiao8372]

ISNULL，COALESCE