how to retrieve mysql data in vb.net?

问题:

im trying to retrieve mysql data with specific column and show to textbox in vb.net. what should i do in retrieving it?

Dim connect As New MySqlConnection("server=localhost; user id=root; password= ; database=ticketing_system;")
    connect.Open()

    Dim sqladapter As New MySqlDataAdapter
    Dim sqlcmd As New MySqlCommand
    Dim dr As MySqlDataReader
    Dim dt As New DataTable

    sqlcmd = New MySqlCommand("SELECT * complaint WHERE tran_no='" & lbltranno.Text & "'")
    **THEN? WHAT SHOULD I DO TO DISPLAY DATA? PLEASE HELP**

    connect.Close()

回答1:

Imports System.Data.SqlClient
Public Class Form1
Dim c As New SqlConnection("Data Source=SONY;Initial Catalog=msdb;Integrated Security=True")
Dim cmd As New SqlCommand
Dim da As New SqlDataAdapter
Dim dr As SqlDataReader
Dim ds, ds1 As New DataSet
Private Sub btnsub_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles      btnsub.Click
    Try
        ds.Clear()
        c.Open()
        cmd = New SqlCommand("select Sub_Name from Subject_Detail WHERE Course='" + txtcourse.Text + "'", c)
        da = New SqlDataAdapter(cmd)
        da.Fill(ds, "Subject_Detail")
        Label1.Text = ds.Tables(0).Rows(0).Item(0)
        Label2.Text = ds.Tables(0).Rows(1).Item(0)
        Label3.Text = ds.Tables(0).Rows(2).Item(0)
        Label4.Text = ds.Tables(0).Rows(3).Item(0)
        Label5.Text = ds.Tables(0).Rows(4).Item(0)
        Label6.Text = ds.Tables(0).Rows(5).Item(0)
    Catch ex As Exception
        MsgBox(ex.Message)
    Finally
        c.Close()
    End Try
End Sub
End Class

'This code display all subject name from the table into labels.This might be helped.

回答2:

You are simply missing the Execution method. It depends on what kind of result you want. If you only want the first result from the query (first row and first column) then use sqlcmd.ExecuteScalar().

If you want all the results you'll have to load that into a MySqlDataReader using the method sqlcmd.ExecuteReader()

Using ExecuteReader() :

Dim connect As New MySqlConnection("server=localhost; user id=root; password= ; database=ticketing_system;")
connect.Open()

Dim sqladapter As New MySqlDataAdapter
Dim sqlcmd As New MySqlCommand
Dim dr As MySqlDataReader
Dim dt As New DataTable

sqlcmd = New MySqlCommand("SELECT * complaint WHERE tran_no='" & lbltranno.Text & "'")
dr = sqlcmd.ExecuteReader()
dt.Load(dr)
'Useable datatable in dt variable...

connect.Close()

Using ExecuteScalar() :

Dim connect As New MySqlConnection("server=localhost; user id=root; password= ; database=ticketing_system;")
connect.Open()

Dim sqladapter As New MySqlDataAdapter
Dim sqlcmd As New MySqlCommand
Dim dr As String
Dim dt As New DataTable

sqlcmd = New MySqlCommand("SELECT [COLUMN NAME] complaint WHERE tran_no='" & lbltranno.Text & "'")
dr = sqlcmd.ExecuteScalar()
'dr now contains the value of [COLUMN NAME] for the first returned row.

connect.Close()

回答3:

You can try this:

Dim connString As String = "server=localhost; user id=root; password= ; database=ticketing_system;"
Dim sqlQuery As String = "SELECT * complaint WHERE tran_no='" & lbltranno.Text & "'";
Using sqlConn As New MySqlConnection(connString)
    Using sqlComm As New MySqlCommand()
        With sqlComm
            .Commandtext = sqlQuery
        End With
        Try
            sqlConn.Open()
            Dim sqlReader As MySqlDataReader = sqlComm.ExecuteReader()
            While sqlReader.Read()
                Label1.Text = sqlReader("Name").ToString()
                Label2.Text = sqlReader("Points").ToString()
            End While
        Catch ex As MySQLException
            ' add your exception here '
        End Try
    End Using
End Using

回答4:

Imports MySql.Data.MySqlClient 


''--- Data Reader Example 

private _cn as New MySqlConnection( _ 
"data source=server; database=databaseName; user id=username; password=password") 
private cmd as new MySqlCommand 
private dr as MySqlDataReader 

With cmd 
.Command = "select Name, Address from Clients" 
.CommandType = CommandType.Text 
.Connection = cn 
End With 

cn.Open() 

dr = cmd.ExecuteReader 

While dr.Read 
   '' use dr(0) for get Name, and dr(1) to get Address for this example
   Console.WriteLine(dr(0) & " - " & dr(1)) 
   Console.WriteLine(dr("Name").ToString() & " - " & dr("Address").ToString())       

End While 

dr.Close 
cn.Close 

回答5:

Try this one, i always use this code, that's why i'm pretty sure that this will work...

Imports MySql.Data
Imports MySql.Data.MySqlClient

Dim connect As New MySqlConnection("server=localhost;uid=root;database=ticketing_system;pwd=;")

connect.Open()

Dim sqlcmd As New MySqlCommand("SELECT * complaint WHERE tran_no='" & lbltranno.Text & "'")
Dim sqladapter As New MySqlDataAdapter(sqlcmd)
Dim dt As New DataTable
sqladapter.Fill(dt)

Datagridview1.Datasource = dt

connect.Close()

回答6:

Imports MySql.Data

Imports MySql.Data.MySqlClient

Dim dbConnection As New MySqlConnection("server=localhost;uid=youruser;database=yourdb;pwd=password")

try
dbConnection.open
catch ex as exception
debug.print(ex.message)
end try

using Adapter as new mysqldataadapter("select * from yourtable where yourcolumn = 'yourvalue'", dbConnection)
   using Table as new datatable
     Adapter.fill(Table)
         Datagridview.datasource = table
   end using
end using

dbConnection.close

回答7:

    Dim MysqlConn As MySqlConnection
    Dim connectionString As String = "Server=-host-ip-;Database=Mysqldb;Uid=user;Pwd=password"
    MysqlConn = New MySqlConnection(connectionString)
    Try

        Dim Mysqlcmd As New MySqlCommand("SELECT * FROM Mysqldb.table WHERE col='" & Label6.Text & "'", MysqlConn)
        Dim dt As New DataTable
        Dim Mysqladapter As New MySqlDataAdapter()
        MysqlConn.Open()
        Mysqladapter.SelectCommand = Mysqlcmd

        Mysqladapter.Fill(dt)

        DataGridView1.DataSource = dt
        MessageBox.Show("Connection to Database has been opened.")

        MysqlConn.Close()

    Catch myerror As MySqlException

        MessageBox.Show("Cannot connect to database: " & myerror.Message)

    Finally

        MysqlConn.Dispose()

    End Try

The key is to add the connection at the end of the mysql query as in line 6

回答8:

I used a variation of the code given in this thread with Visual Basic 2015. I found I needed a 2nd argument in the MySqlCommand statement, namely the MySqlConnection variable ("connect" in some of the examples). See thread: Connection must be valid and open VB.Net

Thanks for the help.