股票计算 vb.net 和 sql

Question

我的代码正在运行，但我认为还有另一种方法可以仅使用 sql。我正在考虑将这段代码简化为更简单。请帮忙 代码获取库存表的总和，然后从相同大米名称的事务表中减去，然后显示结果。但如果第二个查询为空，则显示第一个查询的结果，而无需从第二个查询中减去。

 Dim commnd2 As New SqlCommand("SELECT RICETYPE.RICENAME, Sum(STOCK.NUMBEROFSTOCKS) AS SumOfNUMBEROFSTOCKS FROM SUPPLIER INNER JOIN (RICETYPE INNER JOIN STOCK ON RICETYPE.ID = STOCK.RICETYPEID) ON SUPPLIER.ID = STOCK.SUPPLIER GROUP BY RICETYPE.RICENAME", cn)
    dr = commnd2.ExecuteReader()
    If dr.HasRows Then
        While dr.Read
            Dim commnd3 As New SqlCommand("SELECT RICETYPE.RICENAME, Sum(TRANSAC.NUMBEROFSALES) AS SumOfNUMBEROFSALES
            FROM RICETYPE INNER JOIN TRANSAC ON RICETYPE.ID = TRANSAC.RICETYPEID WHERE RICETYPE.RICENAME = '" & dr.Item(0) & "'
            GROUP BY RICETYPE.RICENAME
            ", cn)
            dr2 = commnd3.ExecuteReader()
            If dr2.HasRows Then
                While dr2.Read
                    dt.Rows.Add(dr2.GetValue(0), dr.GetValue(1) - dr2.GetValue(1), dr2.GetValue(1))
                End While
            Else
                dt.Rows.Add(dr.GetValue(0), dr.GetValue(1), 0)
            End If
        End While
    End If

Answer 1

这是使用嵌套求和作为单个查询的一种方法。

SELECT RTO.RICENAME, Sum(ST.NUMBEROFSTOCKS) AS SumOfNUMBEROFSTOCKS, (SELECT Sum(TRANSAC.NUMBEROFSALES) AS SumOfNUMBEROFSALES
            FROM RICETYPE RTI INNER JOIN TRANSAC T ON RTI.ID = T.RICETYPEID WHERE RTI.RICENAME = RTO.RICENAME) 
FROM SUPPLIER S INNER JOIN (RICETYPE RTO INNER JOIN STOCK ST ON RTO.ID = ST.RICETYPEID) ON S.ID = ST.SUPPLIER GROUP BY RTO.RICENAME

RTI 是 RICETYPE 的内部引用，RTO 是外部引用。