代码没有错误，但它没有恢复数据库

Question

这是我的vb.net恢复SQL Server数据库的代码，我认为代码没有包含错误，所以执行代码时似乎没有错误，但并没有恢复数据库。

请帮我找出错误。我在网上搜索了很多，但没有找到任何解决问题的方法。

Sub restore_db()
    Dim con As New SqlConnection("Data Source=HP;Database=Master;integrated security=SSPI;")
    con.Open()
    Dim filename As String
    Dim strQuery As String

    Dim objdlg As New OpenFileDialog
    objdlg.FileName = "service_station"
    objdlg.Filter = "SQL Server database backup files|*.bak"
    objdlg.ShowDialog()

    filename = objdlg.FileName

    strQuery = "ALTER DATABASE service_station set SINGLE_USER WITH ROLLBACK IMMEDIATE"
    strQuery = "RESTORE DATABASE service_station FROM disk='" & filename & "' WITH REPLACE,RECOVERY"
    strQuery = "ALTER DATABASE service_station SET MULTI_USER WITH ROLLBACK IMMEDIATE"

    Dim cmd As SqlCommand
    cmd = New SqlCommand(strQuery, con)

    cmd.ExecuteNonQuery()
    con.Close()
End Sub

Answer 1

你不断覆盖查询值：

strQuery = "ALTER DATABASE ..."
strQuery = "RESTORE DATABASE ..."
strQuery = "ALTER DATABASE ..."

将导致strQuery 值仅包含最后一个字符串。相反，您需要执行以下操作：

' First query
strQuery = "ALTER DATABASE ..."
Dim cmd As SqlCommand = New SqlCommand(strQuery, con)
cmd.ExecuteNonQuery()

' Second query
strQuery = "RESTORE DATABASE ..."
cmd = New SqlCommand(strQuery, con)
cmd.ExecuteNonQuery()

' Third query
strQuery = "ALTER DATABASE ..."
cmd = New SqlCommand(strQuery, con)
cmd.ExecuteNonQuery()