Question

我有以下代码：

Imports System.Data
Imports System.Data.OleDb
Partial Class Dummy
Inherits System.Web.UI.Page

Dim r As OleDbDataReader
Dim con As OleDb.OleDbConnection
Dim cmd As OleDbCommand
Dim cmd1 As OleDbCommand
Dim prev_ob As New List(Of Int64)
Dim cur_ob As Integer
Dim i As Integer = 0

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click

    con = New OleDb.OleDbConnection("provider=SQLOLEDB;data source=PC;initial catalog=DB1;integrated security=SSPI")
    cmd = New OleDbCommand("select single_column from table1 where date_reqd=(SELECT CONVERT(VARCHAR(10),DATEADD(DD, DATEDIFF(DD, 0, GETDATE()), -1),120))", con)
    con.Open()
    r = cmd.ExecuteReader
    While r.Read
        prev_ob.Add(Val(r.Item(0)))
    End While

    cmd = New OleDbCommand("select column1, column2, date_reqd from table1 where date_reqd=(select CONVERT(varchar(10), GETDATE(),120))", con)
    r = cmd.ExecuteReader
    While r.Read
        For i As Integer = 0 To prev_ob.Count - 1
            cur_ob = Val(prev_ob(i)) + Val(r.Item(0))
            cmd1 = New OleDbCommand("update table1 set column4='" & cur_ob & "' where column2='" & r.Item(1) & "' and date_reqd='" & r.Item(2) & "'", con)
            cmd1.ExecuteNonQuery()
            i += 1
            Exit For
        Next
    End While
    con.Close()
End Sub
End Class

我面临的问题是更新仅针对许多值中的第一个正确发生。计算所有其他值，因此在我的表中更新不正确。我几乎可以肯定，循环是导致问题的原因，但一直无法找到解决方法。请帮我纠正。

Answer 1

看起来这应该是一个UPDATE语句。不幸的是，在没有看到实际的表结构的情况下告诉它是很棘手的。首先，写一个这样的select语句（我希望date_reqd实际上也是一个datetime列）：

SELECT
    *
FROM
    table1 t1a
         inner join
    table1 t1b
         on
             t1a.date_reqd = DATEADD(day,DATEDIFF(day,0,CURRENT_TIMESTAMP),-1) and
             t1b.date_reqd = DATEADD(day,DATEDIFF(day,0,CURRENT_TIMESTAMP),0) and
             /* You need other conditions here if there are multiple rows for the same dates
                - I'm guessing there are since you're trying to write a loop */

使用此查询后，请删除前两行（SELECT *），并将其替换为：

UPDATE
    t1b
SET
    column4 = t1a.single_column + t1b.column1

你应该完成。

Answer 2

我自己拿到了！ :)我需要做的就是：

Dim i as Integer=0  

While r.Read  
    cur_ob = Val(prev_ob(i)) + Val(r.Item(0))  
    cmd1 = New OleDbCommand("update table1 set column4='" & cur_ob & "' where column2='" & r.Item(1) & "' and date_reqd='" & r.Item(2) & "'", con)  
    cmd1.ExecuteNonQuery()  
    cur_ob = 0  
    i += 1  
End While

它有效！感谢您的回答/评论和@Damien_The_Unbeliever，我更改了我的主要查询以包含ORDER BY子句。谢谢你的提示！：）

在循环中操作后，数据库中的值无法正确更新

2 个答案: