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vb.net 中如何使用SQL语句查询数据库
dim
成都创新互联公司自成立以来，一直致力于为企业提供从网站策划、网站设计、成都网站设计、网站制作、电子商务、网站推广、网站优化到为企业提供个性化软件开发等基于互联网的全面整合营销服务。公司拥有丰富的网站建设和互联网应用系统开发管理经验、成熟的应用系统解决方案、优秀的网站开发工程师团队及专业的网站设计师团队。
myselectquery
as
string
=
"select
*
from
表1
where
姓名='小强'"
dim
mycommand
as
new
sqlcommand
(myselectquery,
conn)
'建立一个command控件，conn是你的sqlconnection对象
conn.open()'打开数据连接
dim
myreader
as
sqldatareader'定义一个reader用来读数据
myreader
=
mycommand.executereader()'运行你的查询，结果到myreader
if
myreader.read()
then
'如果查到了数据
msgbox(myreader.getstring(0))
'显示第一个字段
end
if
vb.net 中如何使用SQL语句查询数据库中的数据
1、首先打开Visual Studio 2008代码窗口，添加引用。
2、输入以下代码：Public conn1 As SqlConnection = New SqlConnection 。
3、声明关键字 Public；（因为是全局变量，所以用Public 来声明）。
4、如果SQL 数据库就在本机，则用以下代码连接。
5、如果代码太长，影响可读性，可以用空格加"_"后，回车换行即可。
vb.net中，修改数据库表中的某项记录？
后面要跟上 where 条件 比如update 用户信息表 set 操作权限=@type,密码=@pwd, 用户名=@name where 用户信息表ID=@ID
vb.net数据库操作
参考一下下面这段代码就可以了。
Imports System.Data
'引入数据库操作类命名空间
Imports System.Data.OleDb
'引入ADO.NET操作命名空间
Public Class FrmModifystInfo
Inherits System.Windows.Forms.Form
Public ADOcmd As OleDbDataAdapter
Public ds As DataSet = New DataSet()
'建立DataSet对象
Public mytable As Data.DataTable
'建立表单对象
Public myrow As Data.DataRow
'建立数据行对象
Public rownumber As Integer
'定义一个整型变量来存放当前行数
Public SearchSQL As String
Public cmd As OleDbCommandBuilder
'======================================================
#Region " Windows 窗体设计器生成的代码 "
#End Region
'======================================================
Private Sub FrmModifystInfo_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
'窗体的载入
TxtSID.Enabled = False
TxtName.Enabled = False
ComboSex.Enabled = False
TxtBornDate.Enabled = False
TxtClassno.Enabled = False
TxtRuDate.Enabled = False
TxtTel.Enabled = False
TxtAddress.Enabled = False
TxtComment.Enabled = False '设置信息为只读
Dim tablename As String = "student_Info "
SearchSQL = "select * from student_Info "
ExecuteSQL(SearchSQL, tablename) '打开数据库
ShowData() '显示记录
End Sub
Private Sub ShowData()
'在窗口中的textbox中显示数据
myrow = mytable.Rows.Item(rownumber)
TxtSID.Text = myrow.Item(0).ToString
TxtName.Text = myrow.Item(1).ToString
ComboSex.Text = myrow.Item(2).ToString
TxtBornDate.Text = Format(myrow.Item(3), "yyyy-MM-dd ")
TxtClassno.Text = myrow.Item(4).ToString
TxtTel.Text = myrow.Item(5).ToString
TxtRuDate.Text = Format(CDate(myrow.Item(6)), "yyyy-MM-dd ")
TxtAddress.Text = myrow.Item(7).ToString
TxtComment.Text = myrow.Item(8).ToString
End Sub
Private Sub BtFirst_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtFirst.Click
'指向第一条数据
rownumber = 0
ShowData()
End Sub
Private Sub BtPrev_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtPrev.Click
'指向上一条数据
BtNext.Enabled = True
rownumber = rownumber - 1
If rownumber 0 Then
rownumber = 0 '如果到达记录的首部，行号设为零
BtPrev.Enabled = False
End If
ShowData()
End Sub
Private Sub BtNext_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtNext.Click
'指向上一条数据
BtPrev.Enabled = True
rownumber = rownumber + 1
If rownumber mytable.Rows.Count - 1 Then
rownumber = mytable.Rows.Count - 1 '判断是否到达最后一条数据
BtNext.Enabled = False
End If
ShowData()
End Sub
Private Sub BtLast_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtLast.Click
'指向最后一条数据
rownumber = mytable.Rows.Count - 1
ShowData()
End Sub
Private Sub BtDelete_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtDelete.Click
mytable.Rows.Item(rownumber).Delete() '删除记录
If MsgBox( "确定要删除改记录吗？ ", MsgBoxStyle.OKCancel + vbExclamation, "警告 ") = MsgBoxResult.OK Then
cmd = New OleDbCommandBuilder(ADOcmd)
'使用自动生成的SQL语句
ADOcmd.Update(ds, "student_Info ")
BtNext.PerformClick()
End If
End Sub
Private Sub BtModify_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtModify.Click
TxtSID.Enabled = False '关键字段只读
TxtName.Enabled = True '可读写
ComboSex.Enabled = True
TxtBornDate.Enabled = True
TxtClassno.Enabled = True
TxtRuDate.Enabled = True
TxtTel.Enabled = True
TxtAddress.Enabled = True
TxtComment.Enabled = True
End Sub
Private Sub BtUpdate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtUpdate.Click
If Not Testtxt(TxtName.Text) Then
MsgBox( "请输入姓名！ ", vbOKOnly + vbExclamation, "警告 ")
TxtName.Focus()
Exit Sub
End If
If Not Testtxt(ComboSex.Text) Then
MsgBox( "请选择性别！ ", vbOKOnly + vbExclamation, "警告 ")
ComboSex.Focus()
Exit Sub
End If
If Not Testtxt(TxtClassno.Text) Then
MsgBox( "请选择班号！ ", vbOKOnly + vbExclamation, "警告 ")
TxtClassno.Focus()
Exit Sub
End If
If Not Testtxt(TxtTel.Text) Then
MsgBox( "请输入联系电话！ ", vbOKOnly + vbExclamation, "警告 ")
TxtTel.Focus()
Exit Sub
End If
If Not Testtxt(TxtAddress.Text) Then
MsgBox( "请输入家庭住址！ ", vbOKOnly + vbExclamation, "警告 ")
TxtAddress.Focus()
Exit Sub
End If
If Not IsNumeric(Trim(TxtSID.Text)) Then
MsgBox( "请输入数字学号！ ", vbOKOnly + vbExclamation, "警告 ")
Exit Sub
TxtSID.Focus()
End If
If Not IsDate(TxtBornDate.Text) Then
MsgBox( "出生时间应输入日期格式（yyyy-mm-dd）！ ", vbOKOnly + vbExclamation, "警告 ")
Exit Sub
TxtBornDate.Focus()
End If
If Not IsDate(TxtRuDate.Text) Then
MsgBox( "入校时间应输入日期格式（yyyy-mm-dd）！ ", vbOKOnly + vbExclamation, "警告 ")
TxtRuDate.Focus()
Exit Sub
End If
myrow.Item(0) = Trim(TxtSID.Text)
myrow.Item(1) = Trim(TxtName.Text)
myrow.Item(2) = Trim(ComboSex.Text)
myrow.Item(3) = Trim(TxtBornDate.Text)
myrow.Item(4) = Trim(TxtClassno.Text)
myrow.Item(5) = Trim(TxtTel.Text)
myrow.Item(6) = Trim(TxtRuDate.Text)
myrow.Item(7) = Trim(TxtAddress.Text)
myrow.Item(8) = Trim(TxtComment.Text)
mytable.GetChanges()
cmd = New OleDbCommandBuilder(ADOcmd)
'使用自动生成的SQL语句
ADOcmd.Update(ds, "student_Info ")
'对数据库进行更新
MsgBox( "修改学籍信息成功！ ", vbOKOnly + vbExclamation, "警告 ")
TxtName.Enabled = False
ComboSex.Enabled = False
TxtBornDate.Enabled = False
TxtClassno.Enabled = False
TxtRuDate.Enabled = False
TxtTel.Enabled = False
TxtAddress.Enabled = False
TxtComment.Enabled = False '重新设置信息为只读
End Sub
Private Sub BtCancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtCancel.Click
TxtSID.Enabled = False
TxtName.Enabled = False
ComboSex.Enabled = False
TxtBornDate.Enabled = False
TxtClassno.Enabled = False
TxtRuDate.Enabled = False
TxtTel.Enabled = False
TxtAddress.Enabled = False
TxtComment.Enabled = False
End Sub
Public Function ExecuteSQL(ByVal SQL As String, ByVal table As String)
Try
'建立ADODataSetCommand对象
'数据库查询函数
ADOcmd = New OleDbDataAdapter(SQL, "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=c:\student.mdb ")
'建立ADODataSetCommand对象
ADOcmd.Fill(ds, table) '取得表单
mytable = ds.Tables.Item(0) '取得名为table的表
rownumber = 0 '设置为第一行
myrow = mytable.Rows.Item(rownumber)
'取得第一行数据
Catch
MsgBox(Err.Description)
End Try
End Function
End Class
一对多关联的数据库在VB.NET中如何新增记录
script type="text/javascript" src="" /script
script type="text/javascript" src="" /script
有两个表order(orderid,ordername,totalprice), orderdetail(orderid,productid,productname,price) 已经建立一对多
关联(orderid). 用VB.NET建立一个窗体, 用于主表和明细表的数据录入及更新.
在窗体上增加两个sqldataadapter,分别选择order和orderdetail表, 并生成数据集,在DATASET中建立关联(orderid) 主表中:ORDERID,ORDERNAME 绑定在两个TEXTBOX文本框中,用于接受用户的输入,totalprice接受明细表中price
的汇总值.
明细表绑定到一个DATAGRID控件, datasource:dsorder; datamember:order.orderorderdetail建立的关联名称
问题: 在主表中新增一个记录,用户录入orderid和ordername后,进入明细表的录入,用户录入productid, productname, price后,提示 “明细orderID列不允许空值，要更正该值吗？” 是什么原因?
用于连接主表的明细orderID如果输入跟主表一样的orderID时提示“ForeignKeyconstraint 要求在交叉表中存在子键值。要更正该值吗？”
只有录入主表中的orderid和ordername后, 先更新主表数据源,才可以编辑更新明细表,这是为什么? 请问,有没有其他更好的方法, 实现主表和明细表的新增记录同时更新呢? 谢谢关照！ 网友：方宇 回复：
附部分源代码:
Public Class fmOrders
Inherits System.Windows.Forms.Form
Dim WithEvents dtOrderDetails As New DataTable()
Dim BmOrders As BindingManagerBase
Dim BmOrderDetails As BindingManagerBase
Dim OrderDetailsHasChange As Boolean
Dim orderid As DataColumn
dim ordername as datacolumn
Dim SubTotal As DataColumn Private Sub bnFirst_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bnFirst.Click
BmOrders.Position = 0
End Sub
Private Sub bnPrior_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bnPrior.Click
BmOrders.Position -= 1
End Sub
Private Sub bnNext_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bnNext.Click
BmOrders.Position += 1
End Sub
Private Sub bnLast_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bnLast.Click
BmOrders.Position = BmOrders.Count - 1
End Sub Private Sub bnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bnAdd.Click
Try
BmOrders.EndCurrentEdit()
BmOrders.AddNew()
Catch err As System.SystemException
MessageBox.Show(err.ToString)
End Try
End Sub
Private Sub bnLoad_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bnLoad.Click
FillData()
End Sub Private Sub bnUpdate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bnUpdate.Click
Dim dsTestOrdersChange As DataSet BmOrderDetails.EndCurrentEdit()
BmOrders.EndCurrentEdit()
If Not dsTestOrders.HasChanges(DataRowState.Deleted) Then
Try
daOrders.Update(dsTestOrders, "Orders")
daOrderDetails.Update(dsTestOrders, "OrderDetails")
dsTestOrders.AcceptChanges()
Catch err As System.SystemException
dsTestOrders.RejectChanges()
MessageBox.Show(err.ToString)
Throw
End Try
Else
Try
daOrderDetails.Update(dsTestOrders, "OrderDetails")
daOrders.Update(dsTestOrders, "Orders")
dsTestOrders.AcceptChanges()
Catch err As System.SystemException
dsTestOrders.RejectChanges()
MessageBox.Show(err.ToString)
Throw
End Try
End If
End Sub Private Sub fmOrders_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
FillData()
dtOrderDetails = dsTestOrders.Tables("OrderDetails")
BmOrders = Me.BindingContext(dsTestOrders, "Orders")
BmOrderDetails = Me.BindingContext(dsTestOrders, "Orders.OrdersOrderDetails")
OrderDetailsHasChange = True
SubTotal = dsTestOrders.Tables("Orders").Columns("SubTotal")
SubTotal.DefaultValue = 0
Price = dsTestOrders.Tables("OrderDetails").Columns("Price")
Price.DefaultValue = 0
End Sub Private Sub FillData()
dsTestOrders.EnforceConstraints = False
daOrders.Fill(dsTestOrders)
daOrderDetails.Fill(dsTestOrders)
dsTestOrders.EnforceConstraints = True
End Sub
Private Sub dtOrderDetails_ColumnChanged(ByVal sender As Object, ByVal e As System.Data.DataColumnChangeEventArgs) _
Handles dtOrderDetails.ColumnChanged Dim drOrders As DataRow
Dim drOrderDetails As DataRow
Dim iSubTotal As Integer
Try
If OrderDetailsHasChange Then
OrderDetailsHasChange = False
drOrders = dsTestOrders.Tables("Orders").Rows(BmOrders.Position)
iSubTotal = 0
For Each drOrderDetails In drOrders.GetChildRows("OrdersOrderDetails")
iSubTotal = iSubTotal + drOrderDetails("price")
Next
drOrders.BeginEdit()
drOrders("SubTotal") = iSubTotal
drOrders.EndEdit()
End If
Finally
OrderDetailsHasChange = True
End Try
End Sub Private Sub bndelete_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bndelete.Click
If BmOrders.Count 0 Then
BmOrders.RemoveAt(BmOrders.Position)
End If
End Sub Private Sub bncancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bncancel.Click
BmOrders.CancelCurrentEdit() End Sub
End Class script type="text/javascript" src="" /script
script type="text/javascript" src="" /script
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