Question

VB.NET连接Access数据库查找ID最大的前两个数据，或新入库的前两个数据

目前采用OleDbConnection,OleDbReader和OleDbCommand, dr=cmd.ExecuteReader cmd.CommandText="Select top 2 字段名 from 表名 Order by ID DESC"那么t1.Text=dr(0)是ID最大的数，第二大的怎么写？dr(1)就提示错误了

Answer 1

见下面的代码，自己换成真实的数据库及表即可

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Imports System.Data
Imports System.IO
Imports System.Data.OleDb
Module Module1
Public cn1 As New OleDb.OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\ACCESS数据库1.mdb") '定义连接1---这里请更改为实际数据库路径及名称
Public cn2 As New OleDb.OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\ACCESS数据库2.mdb") '定义连接2---这里请更改为实际数据库路径及名称
Public DataBaseRST1 As Integer '用来返回数据库执行结果
Public DataBaseRST2 As Integer '用来返回数据库执行结果
Public Function DataModify(ByVal str_cmd1 As String, ByVal str_cmd2 As String) As Boolean '进行数据库修改操作函数
Dim cmdinsert1 As New OleDbCommand
Dim cmdinsert2 As New OleDbCommand
Try
cmdinsert1.CommandText = str_cmd1
cmdinsert2.CommandText = str_cmd2
cmdinsert1.Connection = cn1
cmdinsert2.Connection = cn2
If cn1.State = ConnectionState.Closed Then cn1.Open()
If cn2.State = ConnectionState.Closed Then cn2.Open()
DataBaseRST1 = cmdinsert1.ExecuteNonQuery() '用来返回执行的结果
DataBaseRST2 = cmdinsert2.ExecuteNonQuery() '用来返回执行的结果
cn1.Close()
cn2.Close()
Return True
Catch ex As Exception
MessageBox.Show(Err.Description, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
Return False
End Try
End Function
End Module
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
DataModify("insert into aa values ('1','2')", "insert into aa values ('1','2')") '调用方法
End Sub
End Class

追问
这个方法我只能用于添加修改删除，请问，查询数据并且绑定到DGV怎么做？

回答
Public Function Search(ByVal cn1 As OleDb.OleDbConnection, ByVal cn2 As OleDb.OleDbConnection, ByVal str_cmd1 As String, ByVal str_cmd2 As String, ByVal DGV1 As DataGridView, ByVal DGV2 As DataGridView) As Boolean '查询 str_cmd1,str_cmd2---查询命令，DGV1,DGV2---DataGridView，用来显示数据的控件
Dim tb1 As New DataTable
Dim tb2 As New DataTable
Try
Dim ap1 As New OleDb.OleDbDataAdapter(str_cmd1, cn1)
ap1.Fill(tb1)
DGV1.DataSource = tb1
Dim ap2 As New OleDb.OleDbDataAdapter(str_cmd2, cn2)
ap2.Fill(tb2)
DGV2.DataSource = tb2
Return True
Catch ex As Exception
MessageBox.Show(Err.Description, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
Return False
End Try

Answer 2

dr.read()

t2.text=dr(0)

追问

dr(0)是ID最大的数据，那第二大的怎么表示，dr(1)提示超出数组界限，数组大小在哪表现的？

追答

看不懂啊？
你往小读一个，再取dr(0)

dr.read()'使用它往下读一个
这时dr(0)就是第二大的数