vb.net 連接SQL數據庫登錄代碼

問題應該出在你的查詢語句的結果沒有值,你用你的查詢語句到SQL中是否有返回值?記得加上你的條件,另外,你語句里這一句是多余的.Dim s As Object = sComm.ExecuteScalar 以下語句測試正常 Dim myCn As New SqlClient.SqlConnection Try myCn.ConnectionString = sConnString myCn.Open() Dim mySQL As String = "SELECT * FROM ygzl" Dim sComm As New SqlClient.SqlCommand(mySQL, myCn) If sComm.ExecuteScalar Then Dim User_MainForm As New Form1 User_MainForm.Show() Else MsgBox("用戶名或密碼不正確，請重試！") End If Catch ex As Exception MsgBox(ex.Message) Finally myCn.Close() '關閉連接 End Try

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求VB.NET2010操作ACCESS數據庫的完整代碼

Imports System.Data.OleDb

Public Class Parking

Private Sub Parking_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Now_Timer.Enabled = True

End Sub

Private Sub Now_Timer_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Now_Timer.Tick

Now_Time_Label.Text = "當前時間：" Date.Now

End Sub

Private Sub Enter_Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Enter_Button.Click

'定義一個OLEDB連接字符串

Dim conStr As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=F:\test\test.mdb"

'實例化OLEDB連接

Dim con As OleDbConnection = New OleDbConnection(conStr)

Dim sql As New System.Text.StringBuilder

'定義數據庫插入語句

sql.Append("insert into Time_billing([Car_Num],[Enter_Time])")

sql.Append("values('" Trim(Car_Num_Text.Text) "','" Date.Now "')")

'打開數據庫鏈接

con.Open()

'定義執行命令

Dim cmd As New System.Data.OleDb.OleDbCommand(sql.ToString, con)

'執行命令

cmd.ExecuteNonQuery()

'關閉數據庫鏈接

con.Close()

MsgBox("提交成功！")

End Sub

Private Sub Leave_Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Leave_Button.Click

Dim Time_Length As Double

Dim Pack_Fee As Double

Dim Enter_time As Date

Dim Leave_time As Date

Dim conStr As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=F:\test\test.mdb"

Dim con As OleDbConnection = New OleDbConnection(conStr)

Dim selSql As New System.Text.StringBuilder

Dim inSql As New System.Text.StringBuilder

Dim upSql As New System.Text.StringBuilder

Dim delSql As New System.Text.StringBuilder

Dim dr As OleDbDataReader

con.Open()

'SQL拼接過程中最后不需要有分號

'在賦值時，讀取字段值時必須使用在數據庫客戶端查詢時顯示的字段名

selSql.Append("select")

selSql.Append(" Enter_Time")

selSql.Append(" from [Time_billing]")

selSql.Append("where Car_Num = '").Append(Trim(Car_Num_Text.Text)).Append("'")

Dim selcmd As New OleDb.OleDbCommand(selSql.ToString, con)

dr = selcmd.ExecuteReader()

If dr.Read() Then

Enter_time = dr("Enter_Time")

Leave_time = Date.Now

Else

MsgBox("木有數據！")

End If

Enter_Time_Text.Text = Enter_time

Leave_Time_Text.Text = Leave_time

'求時間差

Time_Length = Math.Round(DateDiff(DateInterval.Minute, Enter_time, Leave_time) / 60, 2)

Pack_Fee = Time_Length * 5

Pack_Fee_Text.Text = Pack_Fee

inSql.Append("update [Time_billing]")

inSql.Append(" set [Leave_Time] = '").Append(Trim(Leave_Time_Text.Text)).Append("'")

inSql.Append(" ,[Packing_Fee] = '").Append(Pack_Fee).Append("'")

inSql.Append("where Car_Num = '").Append(Trim(Car_Num_Text.Text)).Append("'")

Dim incom As New OleDb.OleDbCommand(inSql.ToString, con)

incom.ExecuteNonQuery()

'con.Close()

MsgBox("結算完成！")

'con.Open()

upSql.Append("insert into Time_billing_History([Car_Num],[Enter_Time],[Leave_Time],[Packing_Fee])")

upSql.Append(" select")

upSql.Append(" [Car_Num]")

upSql.Append(",[Enter_Time]")

upSql.Append(",[Leave_Time]")

upSql.Append(",[Packing_Fee]")

upSql.Append(" from [Time_billing]")

upSql.Append("where [Car_Num] = '").Append(Trim(Car_Num_Text.Text)).Append("'")

Dim upcom As New OleDb.OleDbCommand(upSql.ToString, con)

upcom.ExecuteNonQuery()

delSql.Append("delete")

delSql.Append(" from")

delSql.Append(" [Time_billing]")

delSql.Append(" where [Car_Num] = '").Append(Trim(Car_Num_Text.Text)).Append("'")

Dim delcom As New OleDb.OleDbCommand(delSql.ToString, con)

delcom.ExecuteNonQuery()

con.Close()

End Sub

Private Sub Clear_Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Clear_Button.Click

Car_Num_Text.Clear()

Enter_Time_Text.Clear()

Leave_Time_Text.Clear()

Pack_Fee_Text.Clear()

End Sub

End Class

vb.net2015連接數據庫SQL2012代碼

1、 用The SQL Server .NET Data Provider連接數據庫

The SQL Server .NET Data Provider是利用SqlConnection類來連接SQL Server7.0或更高版本的數據庫，

SqlConnection類位于名稱空間System.Data.SqlClient下。

連接代碼：

Dim sqlConnection1 As SqlClient.SqlConnection

Dim strConnect As String=”data source=服務器名;initial catalog=數據庫名;user id=sa;password=;”

sqlConnection1=New System.Data.SqlClient.SqlConnection(strConnect)

sqlConnection1.open ‘打開數據庫

sqlConnection1.close ‘關閉連接，釋放資源

2、 用The OLE DB .NET Data Provider連接數據庫

上面已經說過，利用The OLE DB .NET Data Provider可以訪問Access、Oracle和SQL Server等種數據

庫，那么，它是怎樣訪問這些數據庫的呢？The OLE DB .NET Data Provider是通過位于名稱空間Sy

stem.Data.OleDb類庫下的OleDbConnection類來連接這三種不同類型的數據庫的。下面舉例說明:

1)連接SQL Server數據庫

Dim oleDbConnection1 As OleDb.OleDbConnection

Dim strConnect As Sting=”Provider=SQLOLEDB;Persist Security Info=False;Data Source=服務器名;Initial Catalog=數據庫名;User ID=sa;Password=;”

oleDbConnection1=New System.Data.OleDb.OleDbConnection(strConnect)

2)連接Access數據庫

假設要連接的Access數據庫名為“Example.mdb”，存放在d:\Data\目錄下。

Dim oleDbConnection1 As OleDb.OleDbConnection

Dim strConnect As Sting=”Provider=Microsoft.Jet.OLEDB.4.0;Data Source=d:\Data\ Example.mdb”

oleDbConnection1= New System.Data.OleDb.OleDbConnection(strConnect)

3)連接Oracle數據庫

Dim oleDbConnection1 As OleDb.OleDbConnection

Dim strConnect As Sting=”Provider=MSDAORA;Data Source=服務器名;User ID=用戶ID;Password=密碼;”

oleDbConnection1= New System.Data.OleDb.OleDbConnection(strConnect)

3、 用The ODBC .NET Data Provider連接數據庫

The ODBC .NET Data Provider連接數據庫是通過OdbcConnection類來實現的，這個類位于名稱空間

Microsoft.Data.Odbc下，而名稱空間Microsoft.Data.Odbc是封裝在Microsoft.Data.Odbc.dll文件下的。

由于篇幅有限，這里就只介紹連接Sql Server和Oracle數據庫的方法，其他數據庫的連接方法基本類

似，我就不再多講了。

1)連接Sql Server數據庫

Dim odbcDbConnetion1 As Microsoft.Data.OdbcConnection

Dim strConnect As Sting=”Driver={SQL Server};Server=服務器名;Uid=sa;pwd=;Database= 數據庫名;”

odbcDbConnetion1=New Microsoft.Data.OdbcConnection(strConnect)

2)連接Oracle數據庫

Dim odbcDbConnetion1 As Microsoft.Data.OdbcConnection

Dim strConnect As Sting=”Driver={Microsoft ODBC for Oracle};Server=服務器名;Uid=sa;pwd=;”

odbcDbConnetion1=New Microsoft.Data.OdbcConnection(strConnect)

四、總結

通過本文的介紹，讀者基本掌握了在Visual Basic.NET中用ADO.NET和ODBC.NET連接各種數據庫的方法

。以上三種驅動針對不同的數據庫，它們的性能方面也有很大的不同：The SQL Server .NET Data Provider

的效率最高；The OLE DB .NET Data Provider的效率比較底；The ODBC .NET Data Provider的效率最慢。

使用VB.net實現sql數據庫的備份與恢復代碼

Private Sub Button _Click(ByVal sender As System Object ByVal e As System EventArgs) Handles Button Click 備份數據庫 BACKUP DATABASE Test TO DISK= C:\Backup WITH Format Dim cn As SqlConnection Dim cm As SqlCommand cn = getDB() cm = New SqlCommand( BACKUP DATABASE JXbase TO DISK= C:\Backup WITH Format cn) cn Open() cm ExecuteNonQuery() MsgBox( 備份成功 ) cn Close()

End Sub

恢復 Private Sub Button _Click(ByVal sender As System Object ByVal e As System EventArgs) Handles Button Click Dim cn As New SqlConnection Dim cn As New SqlConnection Dim mydr As SqlDataReader Dim str As String

Dim tmpConnectionString As String = Data Source=JJK;Initial Catalog=master;Integrated Security=True cn ConnectionString = tmpConnectionString cn ConnectionString = tmpConnectionString cn Open() cn Open() Dim cm As SqlCommand = New SqlCommand( select spid from master sysprocesses where dbid=db_id( JXbase ) cn) mydr = cm ExecuteReader()

Dim cm As SqlCommand = New SqlCommand() cm Connection = cn

While (mydr Read()) 殺死進程

str = kill mydr( spid ) ToString() cm CommandText = str cm CommandType = CommandType Text Application DoEvents() cm ExecuteNonQuery() 殺進程 End While mydr Close() cm = New SqlCommand( RESTORE DATABASE JXbase FROM DISK= C:\Backup cn) 恢復備份 cm ExecuteNonQuery() MsgBox( 恢復成功成功 ) cn Close() cn Close()

lishixinzhi/Article/program/net/201311/12901

求vb.net的源代碼，最好說明其解決問題，越多越好，滿意加50分。

下面這段代碼，是我用來計算每個月存500元進銀行，連續30年，最后連本帶利能有多少錢。這里面涉及復利計算。界面中右邊的文本框用來輸出每一次計算的結果。

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

? Dim nianxian As Integer '年限變量

? Dim dingcun As Integer '定存變量

? Dim fuli_big As Long '大復利

? Dim fuli_small As Long '小復利

? Dim i As Integer '循環變量

? Dim DATAstring As String '數據字符串

? nianxian = Val(年限_TextBox.Text)

? dingcun = Val(定存_TextBox.Text)

? DATAstring = ""

? For i = 1 To nianxian

? ? ? fuli_small = dingcun * (1 + 0.1875)

? ? ? dingcun = fuli_small

? ? ? fuli_big = fuli_big + fuli_small

? ? ? DATAstring = DATAstring + "[" + Trim(Str(i)) + "]" + Str(fuli_big) + Chr(13) + Chr(10)

? ? ? 'DATAstring = DATAstring + "[" + Trim(Str(i)) + "]" + Str(fuli_small) + Chr(13) + Chr(10)

? Next

? 'fuli_big = fuli_small

? TextBox1.Text = DATAstring

? 結果_TextBox.Text = Str(fuli_big) + "元"

End Sub

VB.NET中的代碼

大概的過程：

Imports System.Data

Imports System.Data.SqlClient

--------------

Dim a As New SqlDataAdapter

Dim con As SqlConnection

con = New SqlConnection( "Persist Security Info=False;Integrated Security=SSPI;database=northwind;server=.;Connect Timeout=30")

con.Open()

a.SelectCommand = New SqlCommand("select * from table where c=1", con)

a.UpdateCommand = New SqlCommand("update table set b=2 where c=1", con)

a.DeleteCommand = New SqlCommand("delete from table where c=1", con)

a.InsertCommand = New SqlCommand("insert into table values (1,2,3)", con)

a.SelectCommand.ExecuteNonQuery()

a.UpdateCommand.ExecuteNonQuery()

a.DeleteCommand.ExecuteNonQuery()

a.InsertCommand.ExecuteNonQuery()

con.Close()

a.Dispose()

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