Mysql 无法看到计算值，可能是因为null

我在这里的代码是要知道我的库存在某个日期范围内的状态，但是当涉及到库存时，我遇到了一个问题，它没有返回任何值

我没有套衫的价值，但它应该计算股票=交货-售出+套衫 这是代码

Select A.prod_name As Product, A.prod_totalPrice As Price, A.prod_category As Category, A.prod_ExpDate As Expiration,
ifnull((Select SUM(itp_needQty) from tbl_itmonpur Where itp_prodID = (Select prod_id from tbl_prod where prod_name = A.prod_name)and itp_statusDelv = 'DELIVERED' and itp_date Between "10/06/2014" and "10/06/2014"),0) As Delivered, 
ifnull((Select SUM(sales_qty) from tbl_sales Where sales_prodID = (Select prod_id from tbl_prod where prod_name = A.prod_name)AND sales_date between"10/06/2014" and "10/06/2014" ),0) As Sold, 
ifnull((Select SUM(po_qty) from tbl_PullOver Where po_prodID = (Select prod_id from tbl_prod where prod_name = A.prod_name) AND po_date between "10/06/2014" and "10/06/2014" ),0) As PullOut, 
ifnull((Select SUM(itp_needQty) from tbl_itmonpur Where itp_prodID = (Select prod_id from tbl_prod where prod_name = A.prod_name)and itp_statusDelv = 'DELIVERED' and itp_date Between "10/06/2014" and "10/06/2014") - ((Select SUM(sales_qty) from tbl_sales Where sales_prodID = (Select prod_id from tbl_prod where prod_name = A.prod_name)AND sales_date between "10/06/2014" and "10/06/2014" ) + (Select SUM(po_qty) from tbl_PullOver Where po_prodID = (Select prod_id from tbl_prod where prod_name = A.prod_name) AND po_date between "10/06/2014" and "10/06/2014")), 0) As Stock,
S.supp_name As Supplier 
From tbl_prod As A 
Inner Join tbl_supp As S 
On A.prod_suppID = S.supp_id 
Group By Product;

我只是个学生，请对我宽容点。谢谢大家!

在MySQL中，您可以使用该函数来处理这种情况：

聚结值，… 返回列表中的第一个非NULL值，如果没有非NULL值，则返回NULL。 例如：

选择合并1、2、3；-将返回1 选择coalescenull，2，3；-将返回2 选择coalesce1，null，3；-将返回1 选择合并空、空、空；-将返回null

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您是否尝试过独立运行每个子查询并查看从中得到的结果？