用于检索数据并将其显示在 vb.net 中的标签中的 MySql 查询

Question

I've researched topics about this but unfortunately I can't find anything that I can easily understand. I have a MySQL database entitled GMASS standing for Guidance Monitoring and Scheduling System. What I want to do is when I input the student number from student table, the name of the student will be previewed in my label. How can I do this?I'm basically a beginner in this. Thank you so much in advance.

Answer 1

Imports System
Imports System.Data
Imports MySql.Data.MySqlClient


Public Class bd


    Public Shared Mystr As String = MyConnectStr.getConnectString("localhost", "root", "", "databasename")


    Public Shared Sub setConnectionString(str As String)
        Mystr = str
    End Sub

    Public Shared Function getConnectionString() As String
        Return Mystr
    End Function


    Public Shared Function Executer_scalar(Query As String) As String
        Dim MySqlConn As MySqlConnection = Nothing
        Try

            MySqlConn = New MySqlConnection(getConnectionString())

            Dim MySqlCom As New MySqlCommand(Query, MySqlConn)

            MySqlConn.Open()

            setNamesUTF8(MySqlConn)



            Return MySqlCom.ExecuteScalar().ToString()
        Catch ex As Exception
            Throw ex
        Finally
            Try
                MySqlConn.Close()
            Catch generatedExceptionName As Exception
            End Try
        End Try
    End Function

    Public Shared Function Executer_NonQuery(Query As String) As Integer
        Dim MySqlConn As MySqlConnection = Nothing
        Try
            MySqlConn = New MySqlConnection(getConnectionString())

            Dim MySqlCom As New MySqlCommand(Query, MySqlConn)

            MySqlConn.Open()

            setNamesUTF8(MySqlConn)



            Return MySqlCom.ExecuteNonQuery()
        Catch ex As Exception
            Throw ex
        Finally
            Try
                MySqlConn.Close()
            Catch ex As Exception
            End Try
        End Try
    End Function

    Public Shared Function Query(q As String, Optional table_name As String = "Table") As DataTable
        Dim MySqlConn As MySqlConnection = Nothing
        Try
            MySqlConn = New MySqlConnection(getConnectionString())

            Dim MySqlCom As New MySqlCommand(q, MySqlConn)

            MySqlConn.Open()

            setNamesUTF8(MySqlConn)

            Dim MySqlda As New MySqlDataAdapter(MySqlCom)

            Dim dt As New DataTable(table_name)

            MySqlda.Fill(dt)


            Return dt
        Catch ex As Exception
            Throw ex
        Finally
            Try
                MySqlConn.Close()
            Catch ex As Exception
            End Try
        End Try
    End Function

    Public Shared Function load_table(table_name As String) As DataTable
        Dim MySqlConn As MySqlConnection = Nothing
        Try
            MySqlConn = New MySqlConnection(getConnectionString())

            Dim MySqlCom As New MySqlCommand("SELECT * FROM " & table_name, MySqlConn)

            MySqlConn.Open()

            setNamesUTF8(MySqlConn)

            Dim MySqlda As New MySqlDataAdapter(MySqlCom)

            Dim dt As New DataTable(table_name)

            MySqlda.Fill(dt)


            Return dt
        Catch ex As Exception
            Throw ex
        Finally
            Try
                MySqlConn.Close()
            Catch ex As Exception
            End Try
        End Try
    End Function

    Public Shared Function load_tables(ParamArray table_name As String()) As DataSet
        Dim MySqlConn As MySqlConnection = Nothing
        Try
            Dim ds As New DataSet()

            Dim MySqlCom As MySqlCommand = Nothing

            Dim MySqlda As MySqlDataAdapter = Nothing

            Dim dt As DataTable = Nothing

            MySqlConn = New MySqlConnection(getConnectionString())



            MySqlConn.Open()

            setNamesUTF8(MySqlConn)

            For i As Integer = 0 To table_name.Length - 1
                MySqlCom = New MySqlCommand("SELECT * FROM " & table_name(i), MySqlConn)
                MySqlda = New MySqlDataAdapter(MySqlCom)
                dt = New DataTable(table_name(i))
                MySqlda.Fill(dt)
                ds.Tables.Add(dt)
            Next


            Return ds
        Catch ex As Exception
            Throw ex
        Finally
            Try
                MySqlConn.Close()
            Catch ex As Exception
            End Try
        End Try
    End Function

    Public Shared Function load_DataSet(Query As String, Optional table_name As String = "Table") As DataSet
        Dim MySqlConn As MySqlConnection = Nothing
        Try
            MySqlConn = New MySqlConnection(getConnectionString())

            Dim MySqlCom As New MySqlCommand(Query, MySqlConn)

            MySqlConn.Open()

            setNamesUTF8(MySqlConn)

            Dim MySqlda As New MySqlDataAdapter(MySqlCom)

            Dim ds As New DataSet()

            MySqlda.Fill(ds, table_name)


            Return ds
        Catch ex As Exception
            Throw ex
        Finally
            Try
                MySqlConn.Close()
            Catch ex As Exception
            End Try
        End Try
    End Function

    Public Shared Function load_DataSet_S(ParamArray Query As String()) As DataSet
        Dim MySqlConn As MySqlConnection = Nothing
        Try
            Dim ds As New DataSet()

            Dim MySqlCom As MySqlCommand = Nothing

            Dim MySqlda As MySqlDataAdapter = Nothing

            Dim dt As DataTable = Nothing

            MySqlConn = New MySqlConnection(getConnectionString())

            MySqlConn.Open()

            setNamesUTF8(MySqlConn)

            For i As Integer = 0 To Query.Length - 1
                MySqlCom = New MySqlCommand(Query(i), MySqlConn)
                MySqlda = New MySqlDataAdapter(MySqlCom)
                dt = New DataTable("Table_" & i)
                MySqlda.Fill(dt)
                ds.Tables.Add(dt)
            Next


            Return ds
        Catch ex As Exception
            Throw ex
        Finally
            Try
                MySqlConn.Close()
            Catch
            End Try
        End Try
    End Function

    Public Shared Function load_ps(ps_name As String, Optional params_name As String() = Nothing, Optional params_value As Object() = Nothing) As DataTable
        Dim MySqlConn As MySqlConnection = Nothing
        Try
            MySqlConn = New MySqlConnection(getConnectionString())

            Dim MySqlCom As New MySqlCommand(ps_name, MySqlConn)

            MySqlCom.CommandType = CommandType.StoredProcedure

            If (params_name IsNot Nothing) And (params_value IsNot Nothing) Then
                For i As Integer = 0 To params_name.Length - 1
                    MySqlCom.Parameters.AddWithValue(params_name(i).Replace("@", ""), params_value(i))
                Next
            End If

            MySqlConn.Open()

            setNamesUTF8(MySqlConn)

            Dim MySqlda As New MySqlDataAdapter(MySqlCom)

            Dim dt As New DataTable(ps_name)

            MySqlda.Fill(dt)


            Return dt
        Catch ex As Exception
            Throw ex
        Finally
            Try
                MySqlConn.Close()
            Catch
            End Try
        End Try
    End Function

    Public Shared Function load_ps_ds(ps_name As String, Optional params_name As String() = Nothing, Optional params_value As Object() = Nothing) As DataSet
        Dim MySqlConn As MySqlConnection = Nothing
        Try
            MySqlConn = New MySqlConnection(getConnectionString())

            Dim MySqlCom As New MySqlCommand(ps_name, MySqlConn)

            MySqlCom.CommandType = CommandType.StoredProcedure

            If (params_name IsNot Nothing) And (params_value IsNot Nothing) Then
                For i As Integer = 0 To params_name.Length - 1
                    MySqlCom.Parameters.AddWithValue(params_name(i).Replace("@", ""), params_value(i))
                Next
            End If

            MySqlConn.Open()

            setNamesUTF8(MySqlConn)

            Dim MySqlda As New MySqlDataAdapter(MySqlCom)

            Dim ds As New DataSet()

            MySqlda.Fill(ds)


            Return ds
        Catch ex As Exception
            Throw ex
        Finally
            Try
                MySqlConn.Close()
            Catch ex As Exception
            End Try
        End Try
    End Function

    Public Shared Function load_Reader(Query As String, Optional table_name As String = "Table") As MySqlDataReader
        Dim MySqlConn As MySqlConnection = Nothing
        Try
            MySqlConn = New MySqlConnection(getConnectionString())

            Dim MySqlCom As New MySqlCommand(Query, MySqlConn)

            MySqlConn.Open()

            setNamesUTF8(MySqlConn)


            Return MySqlCom.ExecuteReader()
        Catch ex As Exception
            Throw ex
        End Try
    End Function

    Public Shared Function Execute_Transact(ParamArray Query As String()) As Object
        Dim MySqlConn As MySqlConnection = Nothing
        Dim tran As MySqlTransaction = Nothing
        Try
            MySqlConn = New MySqlConnection(getConnectionString())

            MySqlConn.Open()

            setNamesUTF8(MySqlConn)

            tran = MySqlConn.BeginTransaction()

            Dim MySqlCom As MySqlCommand() = New MySqlCommand(Query.Length) {}

            For i As Integer = 0 To Query.Length - 1
                MySqlCom(i) = New MySqlCommand(Query(i), MySqlConn)
                MySqlCom(i).Transaction = tran
            Next

            For i As Integer = 0 To Query.Length - 1
                MySqlCom(i).ExecuteNonQuery()
            Next

            tran.Commit()


            Return 0
        Catch ex As Exception
            Try
                tran.Rollback()
            Catch exx As Exception
            End Try
            Throw ex
        Finally
            Try
                MySqlConn.Close()
            Catch ex As Exception
            End Try
        End Try
    End Function

    Private Shared Sub setNamesUTF8(conn As MySqlConnection)
        Try


            Dim MySqlCom As New MySqlCommand("SET NAMES 'utf8'", conn)


            MySqlCom.ExecuteNonQuery()
        Catch ex As Exception
            Throw ex
        End Try
    End Sub

End Class