Trying to read data from database/ showing tables on c#

I'm kind of new to SQL Server/C#.

My teacher thought I should write data to the database using C# using SqlConnection and SqlCommand.

I have a friend who wants me to help her on her project but I have no clue h开发者_如何学Goow to get data from the database or how to show a table from the database.

Hope someone find this question useful, especially the beginners out there. :)

Also, how can I get a specific element in a row?

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If your using windows forms then perhaps you may use DataGridView control - see this very simple tutorial to get you started: http://www.dotnetperls.com/datagridview-tutorial

Similarly for web applications, you may use GridView control - see MSDN for various examples: http://msdn.microsoft.com/en-us/library/aa479339.aspx

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Using the same sqlConnection and SqlCommand and SqlReader objects (Classes) get the data from the database via Select queries and you can show them over a datagrid if you want. Just search SO or google. MSDN has a great examples as well.

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Use this (Search&Replace System.Data.OleDB with System.Data.SqlClient):

    public override System.Data.DataTable GetDataTable(string strSQL)
    {
        System.Data.DataTable dt = new System.Data.DataTable();

        using (System.Data.IDbConnection idb = GetConnection())
        {

            lock (idb)
            {
                try
                {

                    using (System.Data.OleDb.OleDbDataAdapter daQueryTable = new System.Data.OleDb.OleDbDataAdapter(strSQL, (System.Data.OleDb.OleDbConnection) idb))
                    {
                        daQueryTable.Fill(dt);
                    } // End Using daQueryTable
                } // End Try
                catch (Exception ex)
                {
                    Log("cOleDB.GetDataTable(string strSQL)", ex, strSQL);
                } // End Catch
                finally
                {
                    if (idb.State != System.Data.ConnectionState.Closed)
                        idb.Close();
                } // End Finally

            } // End Lock idb

        } // End Using idb

        return dt;
    } // End Function GetDataTable





    public System.Data.IDbConnection GetConnection()
    {
        System.Data.OleDb.OleDbConnection oledbc= new System.Data.OleDb.OleDbConnection(m_ConnectionString.ConnectionString);

        return oledbc;
    }

For a valid connection string, go to: http://www.connectionstrings.com/

Here's a VBish version:

Namespace SQL


    Public Class MS_SQL

        Public Const strDefaultCatalog As String = "AdventureWorks"


        Public Shared Function GetConnectionString(Optional ByRef strIntitialCatalog As String = strDefaultCatalog) As String

            Return strConnectionString
        End Function ' GetConnectionString


        Public Shared Function GetConnection(ByVal strConnectionString As String)
            'GetConnectionString(strDataBaseName)

            Return New System.Data.SqlClient.SqlConnection(strConnectionString)
        End Function


        Public Shared Function GetConnection() As System.Data.IDbConnection
            Static strConnectionString As String = GetConnectionString()

            Return New System.Data.SqlClient.SqlConnection(strConnectionString)
        End Function ' GetConnection


        Public Shared Function TestConnection() As Boolean
            Dim bExceptionOccured As Boolean = False

            Using dbConnection As System.Data.IDbConnection = GetConnection()

                SyncLock dbConnection

                    Try
                        'Console.WriteLine("Connection timout: " + dbConnection.ConnectionTimeout.ToString)
                        If Not dbConnection.State = ConnectionState.Open Then
                            dbConnection.Open()
                        End If
                    Catch ex As Exception
                        bExceptionOccured = True
                        'Log.File.WriteText("Error opening the database connection. Check your connection string and password as well as networking and permissions.")
                        Log.File.WriteText("Fehler beim Öffnen der Datenbankverbindung. Bitte überprüfen Sie den Verbindungsstring und das Passwort, sowie das Netzwerk und Berechtigungen.")
                        'Log.File.WriteText("Exception message:")
                        Log.File.WriteText("Fehlerbeschreibung:")
                        Console.WriteLine(ex.Message)
                        ErrorHandling.Exception.iExitCode = ErrorHandling.Exception.ExitCode.EXIT_DATABASE_NOCONNECT
                        'MsgBox("Connection couldn't be opened.", MsgBoxStyle.Critical)
                        ErrorHandling.Exception.TerminateWithErrorcode(ErrorHandling.Exception.ExitCode.EXIT_DATABASE_NOCONNECT)
                    Finally
                        If Not dbConnection.State = ConnectionState.Closed Then
                            dbConnection.Close()
                        End If
                    End Try

                End SyncLock ' dbConnection

            End Using ' dbConnection

            Return bExceptionOccured
        End Function ' TestConnection


        Public Shared Function GetEmbeddedSQLscript(ByVal strSearchedFileName As String) As String
            Dim ass As System.Reflection.Assembly = System.Reflection.Assembly.GetAssembly(GetType(MS_SQL))

            If String.IsNullOrEmpty(strSearchedFileName) Then
                Throw New ArgumentNullException("strSearchedFileName")
            End If

            Dim strFoundRessourceName As String = Nothing
            For Each strEmbeddedRessourceName As String In ass.GetManifestResourceNames()
                If Not String.IsNullOrEmpty(strEmbeddedRessourceName) Then

                    If strEmbeddedRessourceName.EndsWith(strSearchedFileName, System.StringComparison.OrdinalIgnoreCase) Then
                        strFoundRessourceName = strEmbeddedRessourceName
                        Exit For
                    End If
                    ' Console.WriteLine(strEmbeddedRessourceName)
                End If
            Next

            If String.IsNullOrEmpty(strFoundRessourceName) Then
                Throw New Exception("The script """ + strSearchedFileName + """ is not present in the embedded ressources section.")
            Else
                'Console.WriteLine(strFoundRessourceName)
            End If

            Dim strSQLscript As String = Nothing
            Try
                Using strmRessource As System.IO.Stream = ass.GetManifestResourceStream(strFoundRessourceName)

                    Using srRessourceReader As New System.IO.StreamReader(strmRessource)
                        strSQLscript = srRessourceReader.ReadToEnd()
                        srRessourceReader.Close()
                    End Using

                    strmRessource.Close()
                End Using
            Catch ex As Exception
                Throw
            End Try

            Return strSQLscript
        End Function ' GetEmbeddedSQLscript


        Public Class cParameterStore

            Public Class cParameter
                Public SqlDbType As System.Data.SqlDbType = Nothing
                Protected m_Value As Object = Nothing


                Public Sub New(ByVal dbt As System.Data.SqlDbType, ByVal objValue As Object)
                    Me.SqlDbType = dbt
                    Me.Value = objValue
                End Sub ' Constructor


                Public Property Value() As Object

                    Get
                        Return Me.m_Value
                    End Get

                    Set(ByVal objValue As Object)
                        If objValue IsNot Nothing Then
                            Me.m_Value = objValue
                        Else
                            Me.m_Value = System.DBNull.Value
                        End If
                    End Set

                End Property ' Value

            End Class ' cParameter


            Public m_dictParameters As Dictionary(Of String, cParameter) = Nothing


            Sub New()
                Me.m_dictParameters = New Dictionary(Of String, cParameter)
            End Sub ' Constructor


            Public ReadOnly Property Parameters() As Dictionary(Of String, cParameter)

                Get
                    Return Me.m_dictParameters
                End Get

            End Property ' Parameters


            Public Sub Add(ByVal strKey As String, ByVal dbt As System.Data.SqlDbType, ByVal objValue As Object)
                If String.IsNullOrEmpty(strKey) Then
                    Throw New ArgumentNullException("strKey")
                End If

                If dbt = Nothing Then
                    Throw New ArgumentNullException("dbt")
                End If

                If Not strKey.StartsWith("@") Then
                    strKey = "@" + strKey
                End If

                m_dictParameters.Add(strKey, New cParameter(dbt, objValue))
            End Sub ' Add

        End Class ' cParameterStore


        Public Shared Function GetNewParamterStore() As cParameterStore
            Return New cParameterStore()
        End Function ' GetNewParamterStore



        Public Shared Sub ExecuteSQLreader(ByRef strSQL As String, ByRef strWhich As String, ByRef alSQLqueryReturnList As ArrayList)
            'Dim alSQLqueryReturnList As ArrayList
            'alSQLqueryReturnList = New ArrayList

            Using dbConn As System.Data.IDbConnection = GetConnection()

                SyncLock dbConn

                    Using sqlCMD As System.Data.IDbCommand = dbConn.CreateCommand()

                        Try
                            sqlCMD.CommandText = strSQL

                            If Not dbConn.State = System.Data.ConnectionState.Open Then
                                dbConn.Open()
                            End If

                            Using sdrSQLReader As System.Data.IDataReader = sqlCMD.ExecuteReader(System.Data.CommandBehavior.CloseConnection)
                                While sdrSQLReader.Read()
                                    alSQLqueryReturnList.Add(sdrSQLReader.Item(strWhich).ToString())
                                End While
                            End Using

                        Catch QueryError As Exception
                            'Log.File.WriteText(String.Format("Exception in ExecuteSQLreader: {0}{1}{2}", QueryError.Message, vbCrLf, strSQL))
                            Log.File.WriteText(String.Format("Fehler in ExecuteSQLreader: {0}{1}{2}", QueryError.Message, vbCrLf, strSQL))
                        Finally
                            If Not dbConn.State = System.Data.ConnectionState.Closed Then
                                dbConn.Close()
                            End If
                        End Try

                    End Using ' sqlCMD

                End SyncLock ' dbConn

            End Using ' dbConn

        End Sub ' ExecuteSQLreader


        Public Shared Function ExecuteSQLstmtScalarWithParameter(ByRef strSQL As String, ByVal ParameterStore As cParameterStore) As String
            Dim strReturnValue As String = ""

            Using sqldbConnection As System.Data.IDbConnection = GetConnection()

                SyncLock sqldbConnection

                    Using sqlCMD As System.Data.SqlClient.SqlCommand = sqldbConnection.CreateCommand()
                        sqlCMD.CommandText = strSQL

                        Try
                            'sqlCMD.Parameters.Add("@mandant", System.Data.SqlDbType.Int).Value = 5
                            For Each kvpThisParameter As KeyValuePair(Of String, cParameterStore.cParameter) In ParameterStore.Parameters
                                sqlCMD.Parameters.Add(kvpThisParameter.Key, kvpThisParameter.Value.SqlDbType).Value = kvpThisParameter.Value.Value
                            Next


                            ' Open the connection
                            If Not sqldbConnection.State = ConnectionState.Open Then
                                sqldbConnection.Open()
                            End If

                            Dim objResult As Object = sqlCMD.ExecuteScalar()

                            If objResult IsNot Nothing Then
                                strReturnValue = objResult.ToString()
                            Else
                                strReturnValue = Nothing
                            End If

                            objResult = Nothing
                        Catch ex As System.Data.SqlClient.SqlException
                            'Log.File.WriteText(String.Format("Exception executing ExecuteSQLstmtScalarWithParameter: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                            Log.File.WriteText(String.Format("Fehler beim Ausführen von ExecuteSQLstmtScalarWithParameter: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                            ' No Error notification when silent
                        Finally

                            ' Open the connection
                            If Not sqldbConnection.State = ConnectionState.Closed Then
                                sqldbConnection.Close()
                            End If

                            sqlCMD.Dispose()
                            sqldbConnection.Dispose()
                        End Try

                    End Using ' sqlCMD

                End SyncLock ' sqldbConnection

            End Using ' sqldbConnection

            Return strReturnValue
        End Function ' ExecuteSQLstmtScalarWithParameter


        Public Shared Function ExecuteSQLstmtScalar(ByRef strSQL As String) As String
            Dim strReturnValue As String = ""

            Using sqldbConnection As System.Data.IDbConnection = GetConnection()

                SyncLock sqldbConnection

                    Using sqlCMD As SqlClient.SqlCommand = sqldbConnection.CreateCommand()
                        sqlCMD.CommandText = strSQL

                        Try
                            ' Open the connection
                            If Not sqldbConnection.State = ConnectionState.Open Then
                                sqldbConnection.Open()
                            End If

                            Dim objResult As Object = sqlCMD.ExecuteScalar()

                            If objResult IsNot Nothing Then
                                strReturnValue = objResult.ToString()
                            Else
                                strReturnValue = Nothing
                            End If

                            objResult = Nothing
                        Catch ex As System.Data.SqlClient.SqlException
                            'Log.File.WriteText(String.Format("Exception executing ExecuteSQLstmtScalar: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                            Log.File.WriteText(String.Format("Fehler beim Ausführen von ExecuteSQLstmtScalar: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                            ' No Error notification when silent
                        Finally

                            ' Open the connection
                            If Not sqldbConnection.State = ConnectionState.Closed Then
                                sqldbConnection.Close()
                            End If

                            sqlCMD.Dispose()
                            sqldbConnection.Dispose()
                        End Try

                    End Using ' sqlCMD

                End SyncLock ' sqldbConnection

            End Using ' sqldbConnection

            Return strReturnValue
        End Function ' ExecuteSQLstmtScalar



        Public Shared Sub ExecuteSQLStmtWithParameters(ByRef strSQL As String, ByVal ParameterStore As cParameterStore)

            Using conn As System.Data.IDbConnection = GetConnection()

                SyncLock conn
                    Using sqlCMD As System.Data.SqlClient.SqlCommand = conn.CreateCommand
                        sqlCMD.CommandText = strSQL
                        'sqlCMD.Parameters.Add("@mandant", System.Data.SqlDbType.Int).Value = 5
                        For Each kvpThisParameter As KeyValuePair(Of String, cParameterStore.cParameter) In ParameterStore.Parameters
                            sqlCMD.Parameters.Add(kvpThisParameter.Key, kvpThisParameter.Value.SqlDbType).Value = kvpThisParameter.Value.Value
                        Next

                        'Dim x As System.Data.IDataParameter = cmd.CreateParameter()
                        'x.ParameterName = ""
                        'x.Value = ""
                        'sqlCMD.Parameters.Add(x)


                        Try
                            ' Open the connection
                            If Not conn.State = ConnectionState.Open Then
                                conn.Open()
                            End If

                            sqlCMD.ExecuteNonQuery()

                            'Log.File.WriteText(String.Format("Command ExecuteSQLStmtWithParameters completed successfully. {0}", vbCrLf + "strSQL=" + strSQL))
                        Catch ex As SqlClient.SqlException
                            'Log.File.WriteText(String.Format("Exception executing ExecuteSQLStmtWithParameters: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                            Log.File.WriteText(String.Format("Fehler beim Ausführen von ExecuteSQLStmtWithParameters: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                        Finally
                            If Not conn.State = ConnectionState.Closed Then
                                conn.Close()
                            End If
                        End Try

                    End Using ' sqlCMD

                End SyncLock ' conn

            End Using ' conn

        End Sub ' ExecuteSQLStmtWithParameters


        Public Shared Sub ExecuteSQLStmtNoNotification(ByRef strSQL As String, Optional ByRef strConnectionString As String = Nothing)
            Using conn As System.Data.IDbConnection = GetConnection()

                SyncLock conn

                    Using cmd As System.Data.IDbCommand = conn.CreateCommand()
                        cmd.CommandText = strSQL

                        Try
                            ' Open the connection
                            If Not conn.State = ConnectionState.Open Then
                                conn.Open()
                            End If

                            cmd.ExecuteNonQuery()
                            'Log.File.WriteText(String.Format("Command ExecuteSQLStmtNoNotification completed successfully. {0}", vbCrLf + "strSQL=" + strSQL))
                        Catch ex As SqlClient.SqlException
                            'Log.File.WriteText(String.Format("Exception executing ExecuteSQLStmtNoNotification: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                            Log.File.WriteText(String.Format("Fehler beim Ausführen von ExecuteSQLStmtNoNotification: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                        Finally
                            If Not conn.State = ConnectionState.Closed Then
                                conn.Close()
                            End If
                        End Try

                    End Using ' cmd

                End SyncLock ' conn

            End Using ' conn

        End Sub 'ExecuteSQLStmtNoNotification



        Public Shared Function ExecuteSQLStmtNoNotificationReturnError(ByRef strSQL As String, Optional ByRef strConnectionString As String = Nothing) As System.Data.SqlClient.SqlException
            Dim eErrorCatcher As System.Data.SqlClient.SqlException = Nothing

            Using conn As System.Data.IDbConnection = GetConnection()

                SyncLock conn

                    Using sqlCMD As System.Data.IDbCommand = conn.CreateCommand()

                        Try
                            sqlCMD.CommandText = strSQL

                            ' Open the connection
                            If Not conn.State = System.Data.ConnectionState.Open Then
                                conn.Open()
                            End If

                            sqlCMD.ExecuteNonQuery()
                        Catch ex As System.Data.SqlClient.SqlException
                            eErrorCatcher = ex
                            Log.File.WriteText(String.Format("Fehler beim Ausführen von ExecuteSQLStmtNoNotificationReturnError: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                        Catch ex As Exception
                            Log.File.WriteText(String.Format("Unerwarteter Fehler beim Ausführen von ExecuteSQLStmtNoNotificationReturnError: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                        Finally
                            If Not conn.State = System.Data.ConnectionState.Closed Then
                                conn.Close()
                            End If
                        End Try

                    End Using ' sqlCMD

                End SyncLock ' conn

            End Using ' conn

            Return eErrorCatcher
        End Function 'ExecuteSQLStmtNoNotificationReturnError


        Public Shared Sub ExecuteSQLStmtSilent(ByRef strSQL As String)
            Using conn As System.Data.IDbConnection = GetConnection()

                SyncLock conn

                    Using cmd As System.Data.IDbCommand = conn.CreateCommand()
                        cmd.CommandText = strSQL
                        Try
                            ' Open the connection
                            If Not conn.State = ConnectionState.Open Then
                                conn.Open()
                            End If

                            cmd.ExecuteNonQuery()
                        Catch ex As System.Data.SqlClient.SqlException
                            ' No Error notification in silent mode
                            'Log.File.WriteText(String.Format("Exception executing ExecuteSQLStmtSilent: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                            Log.File.WriteText(String.Format("Fehler beim Ausführen von ExecuteSQLStmtSilent: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                        Finally
                            ' Open the connection
                            If Not conn.State = ConnectionState.Closed Then
                                conn.Close()
                            End If
                        End Try

                    End Using ' cmd

                End SyncLock ' conn

            End Using ' conn

        End Sub 'ExecuteSQLStmtSilent


        Public Shared Sub GetDataSetWithParameters(ByRef strSQL As String, ByRef dsDataFromTable As DataSet, ByRef ParameterStore As cParameterStore)
            GetDataSetWithParameters(strSQL, dsDataFromTable, "ThisTable", ParameterStore)
        End Sub ' GetDataSetWithParameters


        Public Shared Sub GetDataSetWithParameters(ByRef strSQL As String, ByRef dsDataFromTable As DataSet, ByVal strTableName As String, ByRef ParameterStore As cParameterStore)
            Using sqlConnection As System.Data.SqlClient.SqlConnection = GetConnection()

                SyncLock sqlConnection

                    Using sqlCMD As System.Data.SqlClient.SqlCommand = sqlConnection.CreateCommand()
                        sqlCMD.CommandText = strSQL
                        'sqlCMD.Parameters.Add("@mandant", System.Data.SqlDbType.Int).Value = 5
                        Try
                            For Each kvpThisParameter As KeyValuePair(Of String, cParameterStore.cParameter) In ParameterStore.Parameters
                                sqlCMD.Parameters.Add(kvpThisParameter.Key, kvpThisParameter.Value.SqlDbType).Value = kvpThisParameter.Value.Value
                            Next
                        Catch ex As Exception
                            Log.File.WriteText(String.Format("Fehler in GetDataSetWithParameters (at adding parameters): {0}", ex.Message + Environment.NewLine + "strSQL=" + strSQL))
                        End Try

                        Using daQueryTable As System.Data.SqlClient.SqlDataAdapter = New System.Data.SqlClient.SqlDataAdapter(sqlCMD)
                            Try



                                dsDataFromTable = New System.Data.DataSet(strTableName)

                                If Not sqlConnection.State = System.Data.ConnectionState.Open Then
                                    sqlConnection.Open()
                                End If

                                daQueryTable.Fill(dsDataFromTable)
                            Catch ex As Exception
                                'Log.File.WriteText(String.Format("Exception executing GetDataSetWithParameters: {0}", ex.Message + vbCrLf + "strSQL=" + strSQL))
                                Log.File.WriteText(String.Format("Fehler in GetDataSetWithParameters: {0}", ex.Message + Environment.NewLine + "strSQL=" + strSQL))
                            Finally
                                If Not sqlConnection.State = System.Data.ConnectionState.Closed Then
                                    sqlConnection.Close()
                                End If
                            End Try

                        End Using ' daQueryTable

                    End Using ' sqlCMD

                End SyncLock ' sqlConnection

            End Using ' sqlConnection

        End Sub ' GetDataSetWithParameters


        Public Shared Sub GetDataSet(ByRef strSQL As String, ByRef dsDataFromTable As DataSet)
            GetDataSet(strSQL, dsDataFromTable, "ThisTable")
        End Sub ' GetDataSetWithParameters


        Public Shared Sub GetDataSet(ByRef strSQL As String, ByRef dsDataFromTable As DataSet, ByVal strTableName As String)
            Using sqlConnection As System.Data.SqlClient.SqlConnection = GetConnection()

                SyncLock sqlConnection

                    Using daQueryTable As System.Data.SqlClient.SqlDataAdapter = New System.Data.SqlClient.SqlDataAdapter(strSQL, sqlConnection)
                        Try
                            dsDataFromTable = New System.Data.DataSet(strTableName)

                            If Not sqlConnection.State = System.Data.ConnectionState.Open Then
                                sqlConnection.Open()
                            End If

                            daQueryTable.Fill(dsDataFromTable)
                        Catch ex As Exception
                            'Log.File.WriteText(String.Format("Exception executing GetDataSetWithParameters: {0}", ex.Message.ToString() + vbCrLf + "strSQL=" + strSQL))
                            Log.File.WriteText(String.Format("Fehler in GetDataSetWithParameters: {0}", ex.Message + Environment.NewLine + "strSQL=" + strSQL))
                        Finally
                            If Not sqlConnection.State = System.Data.ConnectionState.Closed Then
                                sqlConnection.Close()
                            End If
                        End Try

                    End Using ' daQueryTable

                End SyncLock ' sqlConnection

            End Using ' sqlConnection

        End Sub ' GetDataSet



    End Class


End Namespace

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Very quickly copied from another forum; this should get you started:

From Digital Point Forum:

If you're not looking for paging and updating built in support, just use a repeater, the code should look something like this.

<asp:Repeater id="myRepeater" runat="server">
<ItemTemplate>
<a href='<%# Eval("client_url") %>'><%# Eval("client_name") %> </a>
</ItemTemplate>
</asp:Repeater>

In your Code Behind...

protected void Page_Load(object sender, EventArgs e)
{
    if (IsPostBack == false)
    {
        string strConnection = ConfigurationManager.ConnectionStrings["connectionString"].ConnectionString; // Add your connection string here if you have it in your web.config file, if not, just type it out manually.
        string mySelectQuery = "SELECT client_url, client_name FROM Clients";
        SqlConnection myConnection = new SqlConnection(strConnection);
        SqlCommand myCommand = new SqlCommand(mySelectQuery, myConnection);
        myConnection.Open();
        SqlDataReader myReader;
        myReader = myCommand.ExecuteReader();
        myRepeater.DataSource = myReader;
        myRepeater.DataBind();
        myReader.Close();
        myConnection.Close();
    }
}