如果当前更新的第 0 行，则更新下一行 [英] Update Next Row If Current Updated Row 0

问题描述

我有一张看起来像这样的桌子:

I have a table looks like this :

HarvestID  |  CheckIn | Actual | Status
1          |   Date   | 100    | Process
2          |   Date   | 200    | Process
3          |   Date   | 400    | Process

我的问题是如果我设置了 Qty='350' 然后更新 ID '1' & 如何更新下一行'2' 到 0，ID '3' Qty='350'

and my problem is how to update next row if I set the Qty='350' Then Update ID '1' & '2' to 0, and ID '3' Qty='350'

有没有办法在不创建新表来存储A"数量的总数并使用存储过程的情况下做到这一点?

is there a way to do this without make a new table to stock the Total of 'A' Qty's and using stored procedure ?

我已经尝试过的是:

    cmdTemp = New MySqlCommand("SELECT * FROM tb_harvest ORDER BY CheckIn ASC LIMIT 1", cn)
    sqlrd = cmdTemp.ExecuteReader
    While sqlrd.Read
        harvestid = sqlrd("HarvestID")
        qtyTemp1 = sqlrd("Actual") - Qty : qtyTemp2 = sqlrd("Actual")
    End While
    sqlrd.Close()
    If qtyTemp1 < 0 Then
        cmdTemp = New MySqlCommand("UPDATE tb_harvest SET Actual=0 WHERE HarvestID=" & harvestid & "; " & _
                                   "UPDATE tb_harvest SET Actual=Actual+" & qtyTemp1 & " WHERE HarvestID=" & harvestid + 1, cn)
        cmdTemp.ExecuteNonQuery()
    Else
        cmdTemp = New MySqlCommand("UPDATE tb_harvest SET Actual=Actual-" & qtyTemp2 & " WHERE HarvestID=" & harvestid, cn)
        cmdTemp.ExecuteNonQuery()
    End If

推荐答案

你可以用变量来做到这一点:

You can do this with variables:

set @qty = 350;

update tb_harvest
    set actual = (case when @qty <= 0 then 0
                       when @qty >= actual
                       then if(@qty := @qty - actual, 0, 0)
                       when (@tmp := actual - @qty),
                       then if(@qty := 0, @tmp, @tmp)
                       else actual -- should never happen
                  end)
    order by harvestid;

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